Network Working Group                                       D. Spinellis
Request for Comments: 1947                                     SENA S.A.
Category: Informational                                         May 1996

Greek Character Encoding for Electronic Mail Messages

Status of This Memo

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

Overview and Rational

This document describes a standard encoding for electronic mail [RFC822] containing Greek text and provides implementation guide- lines. The standard is based on MIME [RFC1521] and the ISO 8859-7 character encoding. Although the implementation of this standard is straightforward several non-standard but "functional" - though unlikely to inter-operate - alternatives are in common use. For this reason we highlight common implementation and mail user agent setup errors.

Description

In order to transfer Greek text via electronic mail the text is first translated into the ISO 8859-7 character set, and then encoded using either the Base64 (preferable for text that is mainly Greek) or the Quoted-Printable (justifiable in cases where some Greek words appear inside predominately Latin text) method, as defined in MIME.

The following table provides most common Greek encodings (see also [RFC1345]):

   0646 37 M7 51 MC 23 69 LG L1 G7 GO GC 28 97 Description
   ---- -- -- -- -- -- -- -- -- -- -- -- -- -- -----------
   0386 ea a2 86 cd 71 86                   b6 Capital alpha with acute
   0388 eb b8 8d ce 72 8d                   b8 Capital epsilon with
                                               acute
   0389 ec b9 8f d7 73 8f                   b9 Capital eta with acute
   038a ed ba 90 d8 75 90                   ba Capital iota with acute
   038c ee bc 92 d9 76 92                   bc Capital omicron with
                                               acute
   038e ef be 95 da 77 95                   be Capital upsilon with
                                               acute
   038f f0 bf 98 df 78 98                   bf Capital omega with acute
   0390    c0 a1 fd    a1                   c0 Small iota with acute and
   0391 80 c1 a4 b0 41 a4 61    41 61 41 41 c1 Capital alpha
   0392 81 c2 a5 b5 42 a5 62    42 62 42 42 c2 Capital beta
   0393 82 c3 a6 a1 43 a6 67 23 43 67 43 44 c3 Capital gamma
   0394 83 c4 a7 a2 44 a7 64 40 44 64 44 45 c4 Capital delta
   0395 84 c5 a8 b6 45 a8 65    45 65 45 46 c5 Capital epsilon
   0396 85 c6 a9 b7 46 a9 7a    46 7a 46 49 c6 Capital zeta
   0397 86 c7 aa b8 47 aa 68    47 68 47 4a c7 Capital eta
   0398 87 c8 ac a3 48 ac 75 5c 48 75 48 4b c8 Capital theta
   0399 88 c9 ad b9 49 ad 69    49 69 49 4c c9 Capital iota
   039a 89 ca b5 ba 51 b5 6b    4b 6b 4a 4d ca Capital kappa
   039b 8a cb b6 a4 52 b6 6c 5e 4c 6c 4b 4e cb Capital lamda
   039c 8b cc b8 bb 53 b7 6d    4d 6d 4c 4f cc Capital mu
   039d 8c cd b7 c1 54 b8 6e    4e 6e 4d 50 cd Capital nu
   039e 8d ce bd a5 55 bd 6a 21 4f 6a 4e 51 ce Capital xi
   039f 8e cf be c3 56 be 6f    50 6f 4f 52 cf Capital omicron
   03a0 8f d0 c6 a6 57 c6 70 3f 51 70 50 53 d0 Capital pi
   03a1 90 d1 c7 c4 58 c7 72    52 72 51 55 d1 Capital rho
   03a3 91 d3 cf aa 59 cf 73 5f 53 73 53 56 d3 Capital sigma
   03a4 92 d4 d0 c6 62 d0 74    54 74 54 58 d4 Capital tau
   03a5 93 d5 d1 cb 63 d1 79    55 79 55 59 d5 Capital upsilon
   03a6 94 d6 d2 bc 64 d2 66 5d 56 66 56 5a d6 Capital phi
   03a7 95 d7 d3 cc 65 d3 78    58 78 57 5b d7 Capital chi
   03a8 96 d8 d4 be 66 d4 63 3a 59 63 58 5c d8 Capital psi
   03a9 97 d9 d5 bf 67 d5 76 5b 5a 76 59 5d d9 Capital omega
   03aa    da    ab    91                   da Capital iota with
                                               diaeresis
   03ab    db    bd    96                   db Capital upsilon with
                                               diaeresis
   03ac e1 dc 9b c0 b1 9b                   dc Small alpha with acute
   03ad e2 dd 9d db b2 9d                   dd Small epsilon with acute
   03ae e3 de 9e dc b3 9e                   de Small eta with acute
   03af e5 df 9f dd b5 9f                   df Small iota with acute
   03b0    e0 fc fe    fc                   e0 Small upsilon with acute
                                               and diaeresis
   03b1 98 e1 d6 e1 8a d6       61 41 61 61 e1 Small alpha
   03b2 99 e2 d7 e2 8b d7       62 42 62 62 e2 Small beta
   03b3 9a e3 d8 e7 8c d8       63 47 63 64 e3 Small gamma
   03b4 9b e4 dd e4 8d dd       64 44 64 65 e4 Small delta
   03b5 9c e5 de e5 8e de       65 45 65 66 e5 Small epsilon
   03b6 9d e6 e0 fa 8f e0       66 5a 66 69 e6 Small zeta
   03b7 9e e7 e1 e8 9a e1       67 48 67 6a e7 Small eta
   03b8 9f e8 e2 f5 9b e2       68 55 68 6b e8 Small theta
   03b9 a0 e9 e3 e9 9c e3       69 49 69 6c e9 Small iota
   03ba a1 ea e4 eb 9d e4       6b 4b 6a 6d ea Small kappa
   03bb a2 eb e5 ec 9e e5       6c 4c 6b 6e eb Small lamda
   03bc a3 ec e6 ed 9f e6       6d 4d 6c 6f ec Small mu
   03bd a4 ed e7 ee aa e7       6e 4e 6d 70 ed Small nu
   03be a5 ee e8 ea ab e8       6f 4a 6e 71 ee Small xi
   03bf a6 ef e9 ef ac e9       70 4f 6f 72 ef Small omicron
   03c0 a7 f0 ea f0 ad ea       71 50 70 73 f0 Small pi
   03c1 a8 f1 eb f2 ae eb       72 52 71 75 f1 Small rho
   03c2 aa f2 ed f7 af ed       77 57 72 77 f2 Small final sigma
   03c3 a9 f3 ec f3 ba ec       73 53 73 76 f3 Small sigma
   03c4 ab f4 ee f4 bb ee       74 54 74 78 f4 Small tau
   03c5 ac f5 f2 f9 bc f2       75 59 75 79 f5 Small upsilon
   03c6 ad f6 f3 e6 bd f3       76 46 76 7a f6 Small phi
   03c7 ae f7 f4 f8 be f4       78 58 77 7b f7 Small chi
   03c8 af f8 f6 e3 bf f6       79 43 78 7c f8 Small psi
   03c9 e0 f9 fa f6 db fa       7a 56 79 7d f9 Small omega
   03ca e4 fa a0 fb b4 a0                   fa Small iota with diaeresis
   03cb e8 fb fb fc b8 fb                   fb Small upsilon with
                                               diaeresis
   03cc e6 fc a2 de b6 a2                   fc Small omicron with acute
   03cd e7 fd a3 e0 b7 a3                   fd Small upsilon with acute
   03ce e9 fe fd f1 b9 fd                   fe Small omega with acute

Note: All values are in hexadecimal.

The column headers refer to the following character sets:

0646 The ISO 2DIS 10646 code.

37 PC code page 737 also known as 437G. Note that some implementa- tions of this code page do not include capital letters with acute.

M7 Character set 8859-7 as implemented in Microsoft Windows 3.1,

Microsoft Windows 3.11, and Microsoft Windows 95.

51 IBM code page 851.

MC The Greek code page implemented on the Apple Macintosh computers.

23 IBM code page 423 (EBCDIC-CP-GR).

69 IBM code page 869.

LG Latin Greek (iso-ir-19).

L1 Latin Greek 1 (iso-ir-27). This page only contains the Greek cap-

ital letters whose glyphs do not exist in the Latin alphabet. The other capital letters are rendered using the equivalent Latin let- ter (e.g. "Greek capital letter alpha" is rendered as "Latin capi- tal letter A"). When mapping "Latin Greek 1" text to ISO 8859-7 the Latin capital letters should only be transcribed to the equivalent Greek ones if a suitable heuristic determines that the specific Latin letters are used to represent Greek glyphs.

G7 7 bit Greek (iso-ir-88).

GO Old 7 bit Greek (iso-ir-18).

GC Greek CCITT (iso-ir-150).

28 Character set ISO 5428:1980 (iso-ir-55).

97 The target character set ISO 8859-7:1987 (ELOT-928) (iso-ir-126).

MIME Headers

A mail message that contains Greek text must contain at least the following MIME headers:

MIME-Version: 1.0
Content-type: text/plain; charset=ISO-8859-7
Content-transfer-encoding: BASE64 | Quoted-Printable

In the future, when all email systems implement fully transparent 8-bit e-mail as defined in RFC 1425 and RFC 1426 the message body encoding phase described in this standard will be no longer needed. In this case the requisite MIME headers are modified as follows:
MIME-Version: 1.0
Content-type: text/plain; charset=ISO-8859-7
Content-transfer-encoding: 8BIT
Even when RFC 1425 is used, Q or B encoding will continue to apply to message headers as detailed in the following section.

Optional

It is recommended, although not required, to support Greek encod- ing in mail headers as specified in RFC 1522. Specifically, the B-encoding format is to be the default method used for encoding Greek text in RFC-822 mail headers, and the Q-encoding format the method to use for the exceptional case of encoding a single Greek word or letter in an otherwise Latin-character-based header.

Example

Below is a short example of Quoted-Printable encoded Greek email:

         Date:         Wed, 31 Jan 96 20:15:03 EET
         From:         Diomidis Spinellis <dds@senanet.com>
         Subject:      Sample Greek mail
         To:           Achilleas Voliotis <achilles@theseas.ntua.gr>
         MIME-Version: 1.0
         Content-ID: <Wed_Feb_14_18_49_50_EET_1996_0@senanet>
         Content-Type: Text/plain; charset=ISO-8859-7
         Content-Transfer-Encoding: Base64
         yuHr5+zd8eEsCgrU7yDl6+vn7enq/CDh6/bc4uf07yDh8O/05evl3/Th6SDh8PwgMjYg4/Hc
         7Ozh9OEuCg==

Discussion

It is possible [RFC1428] (and unfortunately common practice) to set up an arrangement of mail user and transfer agents that allow end users to communicate with Greek e-mail messages while violating a number of standards. Such arrangements are unlikely to offer wide scale interoperability.

One common error is to arrange the rendering and composition of Greek messages by rigging a mail user agent hosted in an ISO 8859-1 environment to use a presentation font that contains Greek glyphs and a keyboard input method that generates Greek text using those glyphs. The resulting messages begin with header items indicating contents in the ISO 8859-1 character set and include text in a totally different encoding. Unfortunately this "solution" appears to "work" across similar systems and is widely used.

One other error is to tag Greek text generated on Microsoft Windows platforms as ISO 8859-7 without an intermediate translation phase. It is important to note that the character set used by the Microsoft Windows Greek implementations is NOT the same as the ISO 8859-7 representation. First of all, the character set used to represent Greek characters differs slightly from the ISO 8859-7 encoding (this difference was instrumented in order to rectify the appearance of an early version of Microsoft Word for Windows in which the end-of-section symbol clashed with the "Greek capital alpha with acute" glyph). In addition, a number of 8-bit characters available on Greek Windows implementations are not part of the ISO 8859-7 character set.

Note that the ISO 8859-7 encoding is equivalent to the Greek Standards Organisation ELOT-928 encoding.

References

[ISO-8859] Information Processing -- 8-bit Single-Byte Coded Graphic Character Sets, Part 7: Latin/Greek alphabet, ISO 8859-7, 1987.

[RFC822] Crocker, D., "Standard for the Format of ARPA Internet Text Messages", STD 11, RFC 822, UDEL, August 1982.

[RFC1345] Simonsen, K., "Character Mnemonics & Character Sets" RFC 1345, Rationel Almen Planlaegning, June 1992.

[RFC1425] Klensin, J., Freed N., Rose M., Stefferud E., and D. Crocker, "SMTP Service Extensions", RFC 1425, United Nations University, Innosoft International, Inc., Dover Beach Consulting, Inc., Network Management Associates, Inc., The Branch Office, February 1993.

[RFC1426] Klensin, J., Freed N., Rose M., Stefferud E., and D. Crocker, "SMTP Service Extension for 8bit-MIME Transport", RFC 1426, United Nations University, Innosoft
International, Inc., Dover Beach Consulting, Inc., Network Management Associates, Inc., The Branch Office, February 1993.

[RFC1428] Vaudreuil, G., "Transition of Internet Mail from Just-Send-8 to 8bit-SMTP/MIME", RFC 1428, CNRI, February 1993.

[RFC1521] Borenstein N., and N. Freed, "MIME (Multipurpose Internet Mail Extensions) Part One: Mechanisms for Specifying and Describing the Format of Internet Message Bodies", Bellcore, Innosoft, September 1993.

[RFC1522] Moore K., "MIME Part Two: Message Header Extensions for Non-ASCII Text", University of Tennessee, September 1993.

Security Considerations

Security issues are not discussed in this memo.

Author's Address

Diomidis Spinellis
SENA S.A.
Kyprou 27
GR-152 47 Filothei
GREECE

Phone: +30 (1) 6854535
Fax: +30 (1) 6840631
EMail: D.Spinellis@senanet.com

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