Network Working Group V. Cancio
Request for Comments: 3249 Xerox Corporation
Category: Informational M. Moldovan
G3 Nova Technology, Inc.
H. Tamura
Ricoh Company, LTD.
D. Wing
Cisco Systems
September 2002

Implementers Guide for Facsimile Using Internet Mail

Status of this Memo

This memo provides information for the Internet community. It does
not specify an Internet standard of any kind. Distribution of this
memo is unlimited.

Copyright Notice

Copyright (C) The Internet Society (2002). All Rights Reserved.

Abstract

This document is intended for the implementers of software that use
email to send to facsimiles using RFC2305 and 2532. This is an
informational document and its guidelines do not supersede the
referenced documents.

Table of Contents

1. IntrodUCtion .................................................. 2
1.1 Organization of this document ................................ 2
1.2 Discussion of this document .................................. 2
2. Terminology ................................................... 3
3. Implementation Issues Specific to Simple Mode ................. 3
3.1 Simple Mode Fax Senders ...................................... 3
3.1.1 Multipart-alternative ...................................... 3
3.2 Simple Mode Fax Receivers .................................... 4
3.2.1 Multipart-alternative and Storage Capacity ................. 4
4. Implementation Issues Specific to Extended Mode ............... 4
4.1 Multipart-alternative ........................................ 4
4.2 Correlation of MDN with Original Message ..................... 4
4.3 Correlation of DSN with Original Message ..................... 5
4.4 Extended Mode Receivers ...................................... 5
4.4.1 Confirmation of receipt and processing from User Agents .... 5
4.4.1.1 Discrepancies in MDN [9] Interpretation .................. 5

4.4.1.2 Disposition-Type and body of message in MDN .............. 6
4.4.2 "Subject" of MDN and DSN in Success and Failure Cases ...... 6
4.4.3 Extended Mode Receivers that are MTAs (or ESMTP servers) ... 7
4.4.3.1 Success Case Example ..................................... 7
4.4.3.2 Failure Case Example 1 ................................... 9
4.4.3.3 Failure Case Example 2 ................................... 10
4.4.4 Extended Mode Receivers that are POP3/IMAP4 ................ 11
4.4.4.1 Success Case Example ..................................... 11
4.4.4.2 Failure Case Example ..................................... 12
4.4.5 Receiving Multiple Attachments ............................. 13
5. Implementation Issues Specific to the File Format ............. 13
5.1 IFD Placement & Profile-S Constraints ........................ 13
5.2 Precautions for implementers of RFC2301 [4] ................. 14
5.2.1 Errors encountered during interoperability testing ......... 14
5.2.2 Color Gamut Considerations ................................. 14
5.2.3 File format Considerations ................................. 15
5.2.3.1 Considerations for greater reader flexibility ............ 15
5.2.3.2 Error considerations ..................................... 16
5.3 Content-Type for the file format ............................. 17
6. Implementation Issues for Internet Fax Addressing ............. 17
7. Security Considerations ....................................... 18
8. Acknowledgements .............................................. 18
9. References .................................................... 18
10. Authors' Addresses ........................................... 20
11. Full Copyright Statement ..................................... 21

1. Introduction

This document clarifies published RFCs which standardize facsimile
communications using Internet Email. The intent is to prevent
implementations that deviate in such a way as to cause
interoperability problems.

1.1 Organization of this document

This document contains four sections that clarify, in order, the
handling of simple mode fax messages, extended mode fax messages, the
file format, and the internet addressing of fax recipients.

See Section 2 for terminology.

1.2 Discussion of this document

Discussion of this document should take place on the Internet fax
mailing list hosted by the Internet Mail Consortium (IMC). Please
send comments regarding this document to:

ietf-fax@imc.org

To subscribe to this list, send a message with the body 'subscribe'
to "ietf-fax-request@imc.org".

To see what has gone on before you subscribed, please see the mailing
list archive at:

http://www.imc.org/ietf-fax/

2. Terminology

The following terms are used throughout this document:

DSN - RFC1894, "An Extensible Message Format for
Delivery Status Notifications" [7]
Extended Mode - RFC2532, "Extended Facsimile Using
Internet Mail" [3]
MDN - RFC2298, "An Extensible Message Format for
Message Disposition Notifications" [9]
Simple Mode - RFC2305, "A Simple Mode of Facsimile
Using Internet Mail" [2]
TIFF - profile S or F of "File Format for Internet Fax" [4]
delivered as "image/tiff"
TIFF-FX - other profiles sent as "image/tiff-fx"

In examples, "C:" is used to indicate lines sent by the client, and
"S:" to indicate those sent by the server.

3. Implementation Issues Specific to Simple Mode

Issues specific to Simple Mode [2] are described below:

3.1 Simple Mode Fax Senders

3.1.1 Multipart/alternative

Although a requirement of MIME compliance (16, Section 5.1.4), some
email client implementations are not capable of correctly processing
messages with a MIME Content-Type of "multipart/alternative". If a
sender is unsure if the recipient is able to correctly process a
message with a Content-Type of "multipart/alternative", the sender
should assume the worst and not use this MIME Content-Type.

3.2 Simple Mode Fax Receivers

3.2.1 Multipart/alternative and Storage Capacity

Devices with little storage capacity are unable to cache previous
parts of a multipart/alternative message. In order for such devices
to correctly process only one part of a multipart/alternative
message, such devices may simply use the first part of a
multipart/alternative message it is capable of processing.

This behavior means that even if subsequent, higher-fidelity parts
could have been processed, they will not be used.

This behavior can cause user dissatisfaction because when two high-
fidelity but low-memory devices are used with each other, the
lowest-fidelity part of the multipart/alternative will be processed.

The solution to this problem is for the sender to determine the
capability of the recipient and send only high fidelity parts.
However, a mechanism to determine the recipient capabilities prior to
an initial message sent to the recipient doesn't yet exist on the
Internet.

After an initial message is sent, the Extended Mode mechanism,
described in RFC2532 [3], Section 3.3, enables a recipient to
include its capabilities in a delivery and/or a disposition
notification: in a DSN, if the recipient device is an RFC2532/ESMTP
[3] compliant server or in an MDN if the recipient is a User Agent.

4. Implementation Issues Specific to Extended Mode

Issues specific to Extended Mode [3] fax are described below. Note
that any Extended Mode device also needs to consider issues specific
to Simple Mode (Section 3 of this document).

4.1 Multipart/Alternative

Sections 3.1.1 and 3.2.1 are also applicable to this mode.

4.2. Correlation of MDN with Original Message

To re-iterate a paragraph from section 2.1, RFC2298 [9]:

A message that contains a Disposition-Notification-To header
SHOULD also contain a Message-ID header, as specified in RFC822
[10]. This will permit automatic correlation of MDNs with
original messages by user agents.

4.3 Correlation of DSN with Original Message

Similar to the requirement to correlate an MDN, above, DSNs also need
to be correlated. This is best done using the ENVID parameter in the
"MAIL" command. See Sections 3 and 5.4 of RFC1891 [5] for details.

4.4 Extended Mode Receivers

Confirmation that the facsimile image (attachment) was delivered and
successfully processed is an important ASPect of the extended mode of
the facsimile using Internet mail. This section describes
implementation issues with several types of confirmations.

4.4.1 Confirmation of receipt and processing from User Agents

When a message is received with the "Disposition-Notification-To"
header and the receiver has determined whether the message can be
processed, it may generate a:

a) Negative MDN in case of error, or

b) Positive MDN in case of success

The purpose of receiving a requested MDN acknowledgement from an
Extended Mode recipient is the indication of success or failure to
process the file attachment that was sent. The attachment, not the
body, constitutes the facsimile message. Therefore an Extended Mode
sender would eXPect, and it is recommended that the Extended Mode
receiver send (with an MDN), an acknowledgement of the success or
failure to decode and process the file attachment.

Implementers of the Extended Mode [3] should be consistent in the
feedback provided to senders in the form of error codes and/or
failure/success messages.

4.4.1.1 Discrepancies in MDN [9] Interpretation

An Extended Mode sender must be aware that RFC2298 [9] does not
distinguish between the success or failure to decode the body-content
part of the message and the success or failure to decode a file
attachment. Consequently MDNs may be received which do not reflect
the success or failure to decode the attached file, but rather to
decode the body-content part of the message.

4.4.1.2 Disposition-Type and body of message in MDN

If the receiver of an MDN request is an RFC2532 compliant device
that automatically prints the received Internet mail messages and
attachments, or forwards the attachment via GSTN fax, it should, in
the case of success:

a) Use a "disposition-type" of "dispatched" (with no "disposition-
modifier") in the MDN, and

b) Use text similar to the following in the body of the message:

"This is a Return Receipt for the mail that you sent to [above, or
below, or this address, etc]. The message and attached files[s]
may have been printed, faxed or saved. This is no guarantee that
the message has been read or understood".

and in the case of failure:

a) Use a "disposition-type" of "processed" and disposition-modifier
of "error", and

b) Use text similar to the following in the body of the message:

"This is a Return Receipt for the mail that you sent to [above, or
below, or this address, etc]. An error occurred while attempting
to decode the attached file[s]".

This recommendation adheres to the definition in RFC2298 [9] and
helps to distinguish the returned MDNs for proper handling.

Implementers may wish to consider sending messages in the language of
the sender (by utilizing a header field from the original message) or
including multiple languages, by using multipart/alternative for the
text portion of the MDN.

4.4.2 "Subject" of MDN and DSN in Success and Failure Cases

Because legacy e-mail applications do not parse the machine-readable
headers, e-mail users depend on the human-readable parts of the MDN
to recognize the type of acknowledgement that is received.

Examples:

MDN:
Subject: Your message was processed successfully. (MDN)
Subject: Your message has been rejected. (MDN)

DSN:
Subject: Your message was delivered successfully. (DSN)
Subject: Your message could not be delivered. (DSN)
Subject: Your message is delayed. (DSN)

4.4.3 Extended Mode Receivers that are MTAs (or ESMTP servers)

SMTP server-based implementations are strongly encouraged to
implement the "SMTP Service Extension for Returning Enhanced Error
Codes" [8]. This standard is easy to implement and it allows
detailed standardized success and error indications to be returned to
the sender by the submitting MTA.

The following examples, are provided as illustration only. They
should not be interpreted as limiting the protocol or the DSN form.
If the examples conflict with the definitions in the standards (RFC
1891[5]/1893[6]/1894[7]/2034[8]), the standards take precedence.

4.4.3.1 Success Case Example

In the following example the sender <jean@example.com> sends a
message to the receiver <ifax@example.net> which is an ESMTP server
and the receiver successfully decodes the message.

example.com
+-------+
Mail
User
Agent
+-------+

V
+----------+ +--------+ +---------+
Mail + Mail Mail
Submission----->Transfer---->Transfer
Agent Agent Agent
+----------+ +--------+ +---------+

example.org example.net

SMTP Sequence:

S: 220 example.net SMTP service ready
C: EHLO example.org
S: 250-example.net
S: 250-DSN
S: 250 ENHANCEDSTATUSCODES
C: MAIL FROM:<jean@example.com> RET=HDRS ENVID=MM123456
S: 250 2.1.0 Originator <jean@example.com> ok
C: RCPT TO:<ifax@example.net> NOTIFY=SUCCESS,FAILURE
ORCPT=rfc822ifax@example.net
S: 250 2.1.5 Recipient <ifax@example.net> ok
C: DATA
S: 354 Send message, ending in <CRLF>.<CRLF>
C:
C: [Message goes here.]
C:
C: .
S: 250 2.0.0 Message accepted
C: QUIT
S: 221 2.0.0 Goodbye

DSN (to jean@example.com):

Date: Mon, 12 Dec 1999 19:01:57 +0900
From: postmaster@example.net
Message-ID: <19991212190157.01234@example.net>
To: jean@example.com
Subject: Your message was delivered successfully. (DSN)
MIME-Version: 1.0
Content-Type: multipart/report; report-type=delivery-status;
boundary=JUK199912121854870001

--JUK199912121854870001
Content-type: text/plain

Your message (id MM123456) was successfully delivered
to ifax@example.net.

--JUK199912121854870001
Content-type: message/delivery-status

Reporting-MTA: dns; example.net
Original-Envelope-ID: MM123456
Final-Recipient: rfc822ifax@example.net
Action: delivered
Status: 2.1.5 (Destination address valid)
Diagnostic-Code: smtp; 250 2.1.5
Recipient <ifax@example.net> ok

--JUK199912121854870001
Content-type: message/rfc822

[headers of returned message go here.]

--JUK199912121854870001--

4.4.3.2 Failure Case Example 1

In this example, the receiver determines it is unable to decode the
attached file AFTER it has received the SMTP message. The receiver
then sends a 'failure' DSN.

example.com
+-------+
Mail
User
Agent
+-------+

V
+----------+ +--------+ +---------+
Mail + Mail Mail
Submission----->Transfer---->Transfer
Agent Agent Agent
+----------+ +--------+ +---------+
example.org example.net

SMTP Sequence:

This is the same as the case a). After the sequence, a decode
error occurs at the receiver, so instead of a 'success' DSN, a
'failure' DSN is sent.

DSN (to jean@example.com):

Date: Mon, 12 Dec 1999 19:31:20 +0900
From: postmaster@example.net
Message-ID: <19991212193120.87652@example.net>
To: jean@example.com
Subject: Your message could not be delivered. (DSN)
MIME-Version: 1.0
Content-Type: multipart/report; report-type=delivery-status;
boundary=JUK199912121934240002

--JUK199912121934240002
Content-type: text/plain

Your message (id MM123456) to ifax@example.net resulted in an
error while attempting to decode the attached file.

--JUK199912121934240002
Content-type: message/delivery-status

Reporting-MTA: dns; example.net
Original-Envelope-ID: MM123456
Final-Recipient: rfc822ifax@example.net
Action: Failed
Status: 5.6.1 (Media not supported)
Diagnostic-Code: smtp; 554 5.6.1 Decode error

--JUK199912121934240002
Content-type: message/rfc822

[headers of returned message go here.]

--JUK199912121934240002--

4.4.3.3 Failure Case Example 2

In this example, the receiver determines it is unable to decode the
attached file BEFORE it accepts the SMTP transmission.

SMTP sequence:

S: 220 example.net SMTP service ready
C: EHLO example.org
S: 250-example.net
S: 250-DSN
S: 250 ENHANCEDSTATUSCODES
C: MAIL FROM:<jean@example.com> RET=HDRS ENVID=MM123456
S: 250 2.1.0 Originator <jean@example.com> ok
C: RCPT TO:<ifax@example.net> NOTIFY=SUCCESS,FAILURE
ORCPT=rfc822ifax@example.net
S: 250 2.1.5 Recipient <ifax@example.net> ok
C: DATA
S: 354 Send message, ending in <CRLF>.<CRLF>
C:
C: [Message goes here.]
C:
C: .
S: 554 5.6.1 Media not supported
C: QUIT
S: 221 2.0.0 Goodbye

DSN:

Note: In this case, the previous MTA generates the DSN that is
forwarded to the original sender. The receiving MTA has not
accepted delivery and therefore can not generate a DSN.

4.4.4 Extended Mode Receivers that are POP3/IMAP4

NOTE: This document does not define new disposition-types or
disposition-modifiers. Those used below are defined in RFC
2298[9]. This section provides examples on how POP3/IMAP4 devices
may use the already defined values.

These examples are provided as illustration only. They should not be
interpreted as limiting the protocol or the MDN form. If the
examples conflict with the MDN [9] standard, the standard takes
precedence.

4.4.4.1 Success Case Example

If the original sender receives an MDN which has "displayed",
"dispatched" or "processed" disposition-type without disposition-
modifier, the receiver may have received or decoded the attached file
that it sent. The MDN does not guarantee that the receiver displays,
prints or saves the attached file. See Section 4.4.1.1,
Discrepancies in MDN Interpretation.

NOTE: This example does not include the third component of the
MDN.

Date: 14 Dec 1999 17:48:44 +0900
From: ken_recipient@example.com
Message-ID: <19991214174844.98765@example.com>
Subject: Your message was processed successfully. (MDN)
To: mary@example.net
Mime-Version: 1.0
Content-Type: multipart/report;
report-type=disposition-notification; boundary="61FD1001_IFAX"

--61FD1001_IFAX
Content-Type: text/plain

This is a Return Receipt for the mail that you sent to
"ken_recipient@example.com". The message and attached files may
have been printed, faxed or saved. This is no guarantee that the
message has been read or understood.

--61FD1001_IFAX
Content-Type: message/disposition-notification

Reporting-UA: ken-ifax.example.com; barmail 1999.10
Original-Recipient: rfc822ken_recipient@example.com
Final-Recipient: rfc822ken_recipient@example.com
Original-Message-ID: <19991214174010O.mary@example.net>
Disposition: automatic-action/MDN-sent-automatically; dispatched

--61FD1001_IFAX--

4.4.4.2 Failure Case Example

If the original sender receives an MDN with an "error" or "warning"
disposition-modifier, it is possible that the receiver could not
receive or decode the attached file. Currently there is no mechanism
to associate the disposition-type with the handling of the main
content body of the message or the attached file.

Date: 14 Dec 1999 19:48:44 +0900
From: ken_recipient@example.com
Message-ID: <19991214194844.67325@example.com>
Subject: Your message has been rejected. (MDN)
To: mary@example.net
Mime-Version: 1.0
Content-Type: multipart/report;
report-type=disposition-notification; boundary="84FD1011_IFAX"

--84FD1011_IFAX
Content-Type: text/plain

This is a Return Receipt for the mail that you sent to
"ken_recipient@example.com". An error occurred while attempting
to decode the attached file[s]".

--84FD1011_IFAX
Content-Type: message/disposition-notification

Reporting-UA: ken-ifax.example.com; barmail 1999.10
Original-Recipient: rfc822ken_recipient@example.com
Final-Recipient: rfc822ken_recipient@example.com
Original-Message-ID: <199912141823123.mary@example.net>
Disposition: automatic-action/MDN-sent-automatically;
processed/error

--84FD1011_IFAX
Content-Type: message/rfc822

[original message goes here]

--84FD1011_IFAX--

4.4.5 Receiving Multiple Attachments

A received email message could contain multiple attachments and each
distinct attachment could use TIFF or TIFF-FX with different
encodings or resolutions, and these could be mixed with other file
types.

There is currently no mechanism to identify, in a returned MDN, the
attachments that were successfully decoded from those that could not
be decoded.

If the Extended Mode recipient is unable to decode any of the
attached files, it is recommended that the Extended Mode recipient
return a decoding error for the entire message.

5. Implementation Issues Specific to the File Format

5.1 IFD Placement & Profile-S Constraints

a) An IFD is required, by TIFF 6.0, to begin on a Word boundary,
however, there is ambiguity with regard to the defined size of a
word. A word should be interpreted as a 2-byte quantity. This

recommendation is based on examination of Figure 1 and the
definition of IFD Entry, Bytes 8-11, found in Section 2 of TIFF
6.0.

b) Low memory devices, which support resolutions greater than the
required Profile-S, may be memory-constrained, such that those
devices cannot properly handle arbitrary placement of TIFF IFDs
within a TIFF file.

To interoperate with a receiver that is constrained, it is
strongly recommended that senders always place the IFD at the
beginning of the image file when using any of the Profiles defined
in [4].

5.2 Precautions for implementers of RFC2301 [4]

5.2.1 Errors encountered during interoperability testing

The TIFF/RFC2301 [4] errors listed below were encountered during
interoperability testing and are provided so that implementers of
TIFF readers and writers can take precautionary measures.

a) Although Profile S of TIFF [4] specifies that files should be in
little-endian order, during testing it was found that some common
TIFF writers create big-endian files. If possible, the TIFF
reader should be coded to handle big-endian files. TIFF writers
should always create little-endian files to be compliant with the
standard and to allow interoperation with memory-constrained
devices.

b) Bytes 0-1 of the Image File Header are supposed to be set to "II"
(4949h) or "MM" (4d4dh) to indicate the byte order. During
testing, other values were encountered. Readers should handle
cases where the byte order field contains values other than "II"
or "MM", and writers should ensure the correct value is used.

5.2.2 Color Gamut Considerations

The ITULAB encoding (PhotometricInterpretation = 10) allows choosing
a gamut range for L*a*b* (see the TIFF field Decode), which in turn
provides a way to place finer granularity on the integer values
represented in this colorspace. But consequently, an inadequate
gamut choice may cause a loss in the preservation of colors that
don't fall within the space of colors bounded by the gamut. As such,
it is worth commenting on this.

The ITULAB default gamut, L [0,100] a [-85,85] b [-75,125], was
chosen to accommodate most scan devices, which are typically acquired
from a hardcopy source. It wasn't chosen to deal with the range of
color from camera input or sRGB monitor data. In fact, when dealing
with images from the web and other display oriented sources, the
color range for a scanned hardcopy may likely be inadequate. It is
important to use a gamut that matches the source of the image data.

The following guidelines are recommended:

1. When acquiring input from a printed hardcopy source, without
modification, the ITU-T Recommendation T.42 default ITULAB gamut
should be appropriate.

2. For an sRGB source, the ITU-T Recommendation T.42 default ITULAB
gamut is not appropriate. A more appropriate gamut to consider
is: L [0,100], a [-88,99] and b [-108.8,95.2]. These may be
realized by using the following Decode values for 8-bit data:
(0/1, 100/1, -22440/255, 25245/255, -27744/255, 24276/255).

3. If the range of L*a*b* value can be precomputed efficiently before
converting to ITULAB, then you may get the best result by picking
a gamut that is custom to this range.

5.2.3 File format Considerations

Implementers should make sure of the contents in the following two
sections.

5.2.3.1 Considerations for greater reader flexibility

a) Readers are able to handle cases where IFD offsets point beyond
the end of the file, while writers ensure that the IFD offset does
not point beyond the end of the file.

b) Readers are able to handle the first IFD offset being on a non-
word boundary, while writers ensure that the first IFD offset is
on a word boundary.

c) Readers are flexible and able to accommodate: IFDs that are not
presented in ascending page order; IFDs that are not placed at a
location that precedes the image which the IFD describes; next IFD
offsets that precede the current IFD, the current IFDs' field
data, or the current IFDs' image data. Writers on the other hand
should generate files with IFDs presented in ascending page order;
IFDs placed at a location that precedes the image which the IFD
describes; the next IFD should always follow the current IFD and
all of its data.

d) Writers generate tags with the appropriate type of data (for
example RATIONAL instead of SRATIONAL). Readers are flexible with
those types of misrepresentations that may be readily accommodated
(for example SHORT instead of LONG) and lead to enhanced
robustness.

e) The appropriate count is associated with the tags (it is not 0 and
matches the tag requirement), while readers are flexible with
these types of misrepresentations, which may be readily
accommodated and lead to enhanced robustness.

f) Tags appear in the correct order in the IFD and readers are
flexible with these types of misrepresentations.

5.2.3.2 Error considerations

a) Readers only accept files with bytes 2-3 of the Image File Header
equal to 42 (2Ah), the "magic number", as being valid TIFF or
TIFF-FX files, while writers only generate files with the
appropriate magic number.

b) Files are not generated with missing field entries, and readers
reject any such files.

c) The PageNumber value is based on the order within the Primary IFD
chain. The ImageLayer values are based on the layer order and the
image order within the layer respectively. Readers may reject the
pages where the PageNumber or ImageLayer values are not consistent
with the number of Primary IFDs, number of layers or number of
images within the layers.

d) Tags are unique within an IFD and readers may reject pages where
this is not the case.

e) Strip data does not overlap other file data and the reader may
error appropriately.

f) The strip offset does not point outside the file, under these
conditions readers may reject the page where this is the case.

g) The strip offset + StripByteCounts does not point outside the
file, under these conditions the reader may error appropriately.

h) Only one endian order is used within the file otherwise the
rendered file will be corrupted.

i) Tag values are consistent with the data contained within the image
strip. For example, a bi-level black mark on a white background
image strip with a PhotometricInterpretation tag value of "1" (bit
value of "0" means black) will result in the rendering of the
image as white marks on a black background (reverse video).

j) For the special color spaces (ITULAB, YCBCR, CMYK), the parameters
used for transformations are correct and compliant with the
specification.

k) The XPosition and YPosition values are consistent with the
horizontal and vertical offsets of the top-left of the IFD from
the top-left of the Primary IFD, in units of the resolution. To
do otherwise results in misplacement of the rendered image.

l) All combinations of tag values are correct, with special attention
being given to the sets: XResolution, YResolution and ImageWidth;
PhotometricInterpretation, SamplesPerPixel, and BitsPerSample.
Any appropriate combinations will likely result in image
distortion or an inability to render the image.

m) The appropriate Compression types are used for the image layers
within a Profile M file, such as a bi-level coder for the mask
layers (i.e. odd numbered layers) and multi-level (color) coders
for the background and foreground layers. Readers should reject
files where this is not true.

5.3 Content-Type for the file format

The content-type "image/tiff" should only be used for Profiles S and
F. Some existing implementations based on [4] may use "image/tiff"
for other Profiles. However, this usage is now deprecated. Instead,
the content-type "image/tiff-fx", whose registration is being defined
in [17] should be used.

To maximize interworking with devices that are only capable of
rendering Profile S or F, "image/tiff" SHOULD be used when
transporting Profile S or F.

6. Implementation Issues for Internet Fax Addressing

The "+" and "=" characters are valid within message headers, but must
be encoded within some ESMTP commands, most notably ORCPT [5].
Implementations must take special care that ORCPT (and other ESMTP
values) are properly encoded.

For example, the following header is valid as-is:

To: Home Fax <FAX=+390408565@example.com>

but when used with ORCPT, the "=" and "+" must be encoded like this:

RCPT TO:<FAX=+390408565@example.com>
ORCPT=FAX+3D+2B390408565@example.com

Note the "=" and "+" are valid inside the forward-path, but must be
encoded when used within the esmtp value.

See [5] for details on this encoding.

7. Security Considerations

With regards to this document, Sections 5 in RFC2305 [2] and Section
4 in RFC2532 [3] apply.

8. Acknowledgements

The authors gratefully acknowledge the following persons who
contributed or made comments on earlier versions of this memo:
Claudio Allocchio, Richard Coles, Ryuji Iwazaki, Graham Klyne, James
Rafferty, Kensuke Yamada, Jutta Degener and Lloyd McIntyre.

9. References

[1] Masinter, L., "Terminology and Goals for Internet Fax", RFC
2542, March 1999.

[2] Toyoda, K., Ohno, H., Murai, J. and D. Wing, "A Simple Mode of
Facsimile Using Internet Mail", RFC3205, March 1998.

[3] Masinter, L. and D. Wing, "Extended Facsimile Using Internet
Mail", RFC2532, March 1999.

[4] McIntyre, L., Zilles, S., Buckley, R., Venable, D., Parsons, G.
and J. Rafferty, "File Format for Internet Fax", RFC2301,
March 1998.

[5] Moore, K., "SMTP Service Extension for Delivery Status
Notification", RFC1891, January 1996.

[6] Vaudreuil, G., "Enhanced Mail System Status Codes", RFC1893,
January 1996.

[7] Moore, K. and G. Vaudreuil, "An Extensible Message Format for
Delivery Status Notifications", RFC1894, January 1996.

[8] Freed, N., "SMTP Service Extension for Returning Enhanced Error
Codes", RFC2034, October 1996.

[9] Fajman, R., "An Extensible Message Format for Message
Disposition Notifications", RFC2298, March 1998.

[10] Crocker, D., "Standard for the Format of ARPA Internet Text
Messages", STD 11, RFC822, August 1982.

[11] Postel, J., "A Simple Mail Transfer Protocol", STD 10, RFC821,
August 1982.

[12] Allocchio, C., "Minimal GSTN address format in Internet Mail",
RFC3191, October 2001.

[13] Allocchio, C., "Minimal FAX address format in Internet Mail",
RFC3192, October 2001.

[14] Allocchio, C., "GSTN Address Element Extensions in E-mail
Services", RFC2846, June 2000

[15] Klensin, J., Freed, N., Rose, M., Stefferud, E. and D. Crocker,
D., "SMTP Service Extensions", RFC2846, November 1995

[16] Freed, N. and N. Borenstein, "Multipurpose Internet Mail
Extensions (MIME) Part Two: Media Types", RFC2046, November
1996

[17] McIntyre, L., Parsons, G. and J. Rafferty, "Tag Image File
Format Fax eXtended (TIFF-FX) - image/tiff-fx MIME Sub-type
Registration", RFC3250, September 2002.

[18] Klensin, J., "Simple Mail Transfer Protocol", RFC2821, April
2001.

[19] Resnick, P., "Internet Message Format", RFC2822, April 2001.

10. Authors' Addresses

Vivian Cancio
103 Cuesta Drive
Los Altos, CA 94022

Phone: +1-650-948-3135
EMail: vcancio@pacbell.net

Mike Moldovan
G3 Nova Technology Inc.
5743 Corsa Avenue, Suite 122
Westlake Village, CA 91362

Phone: (818) 865-6600 Ext.113
EMail: mmoldovan@g3nova.com

Hiroshi Tamura
Ricoh Company, LTD.
1-3-6 Nakamagome, Ohta-ku
Tokyo 143-8555 Japan

Phone: +81-3-3777-8124
Fax: +81-3-5742-8859
EMail: tamura@toda.ricoh.co.jp

Dan Wing
Cisco Systems, Inc.
170 W. Tasman Drive
San Jose, CA 95134-1706 USA

Phone: +1-408-525-5314
Fax: +1-408-527-8083
EMail: dwing@cisco.com

11. Full Copyright Statement

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