RFC 3696, "Application Techniques for Checking and Transformation of Names", February 2004

Errata ID: 4002
Status: Held for Document Update
Type: Technical
Publication Format(s) : TEXT
Reported By: Brandon Gabbert
Date Reported: 2014-05-28
Held for Document Update by: Nevil Brownlee
Date Held: 2014-08-25

Section 3 says:

   The exact rule is that any ASCII character, including control
   characters, may appear quoted, or in a quoted string.  When quoting
   is needed, the backslash character is used to quote the following
   character.  For example

      Abc\@def@example.com

   is a valid form of an email address.  Blank spaces may also appear,
   as in

      Fred\ Bloggs@example.com

   The backslash character may also be used to quote itself, e.g.,

      Joe.\\Blow@example.com

   In addition to quoting using the backslash character, conventional
   double-quote characters may be used to surround strings.  For example

      "Abc@def"@example.com

      "Fred Bloggs"@example.com

   are alternate forms of the first two examples above.

It should say:

   The exact rule is that any ASCII character, including control
   characters, may appear quoted, or in a quoted string.  When quoting
   is needed, the backslash character is used to quote the following
   character.  For example

      Abc\@def@example.com

   is a valid form of an email address.  Blank spaces may also appear,
   as in

      Fred\ Bloggs@example.com

   The backslash character may also be used to quote itself, e.g.,

      Joe.\\Blow@example.com

   In addition to quoting using the backslash character, conventional
   double-quote characters may be used to surround strings.  For example

      "Abc@def"@example.com

      "Fred Bloggs"@example.com

      "Joe.\\Blow"@example.com

   are alternate forms of the examples above.

Notes:

Errata 3563 is incorrect. The first two suggested additions it makes to the spec are actually already present in the original spec just one paragraph down. The third and final suggested addition (allowing an unquoted backslash in a quoted string), while appearing to comport with this RFC, violates RFC 2822 (the reference document for this section). While the suggested email address is valid, it is not equivalent to the original.

RFC 2822 sections 3.2.1, 3.2.2, and 3.2.5 define quoted-string as consisting of any unquoted ASCII character except for backslash and double quote, and any backslash-quoted ASCII character including backslash and double quote.

Thus, while it is correct that

"Joe.\Blow"@example.com

is a valid email address, it is not equivalent to

Joe.\\Blow@example.com

as the \B in the first should be interpreted as a quoted B, not as an illegally unquoted backslash followed by a B. The quoted equivalent of

Joe.\\Blow@example.com

is

"Joe.\\Blow"@example.com

This example was probably left out of the original spec because the quoted-string version differs from the original only in the quotes themselves.

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