#language en
== SpamAssassin Rule: MSGID_MULTIPLE_AT ==

''Standard description:'' Message-ID contains multiple '@' characters

=== Explanation ===

The Message-Id: header contains more than one "@" characters, rendering it invalid.  Invalid Message-Id headers have been seen generated by some types of spamming software.

=== Further Info ===

The default scores for this rule can be found [[http://spamassassin.apache.org/tests.html|in the online list of tests]].

The syntax for the Message-Id field is defined in 
[[http://www.apps.ietf.org/rfc/rfc2822.html#sec-3.6.4|RFC 2822 sec 3.6.4]], as well as recommended algorithms.

[[https://issues.apache.org/SpamAssassin/show_bug.cgi?id=5707|Bug #5707]] suggests that ''Microsoft Office Outlook 12.0'' (a.k.a [[http://support.microsoft.com/ph/11335|Office Outlook 2007]]) generates invalid Message-Id fields, triggering this rule.

''Note:'' Since ''{{{dot-atom-text}}}'' does not include the @ symbol, multiple instances usually indicate an invalid Message-Id.  However it is possible for a syntactically valid (per RFC2822) Message-Id field to contain multiple "@" symbols under the circumstances that the ''{{{id-left}}}'' component consists of a double-quoted string (where ''{{{qtext}}}'' can contain ''{{{%d64}}}'', although this format is now marked as obsolete by RFC5322) or inside ''{{{id-right}}}'' as part of a literal address string. For example:
  {{{Message-Id: <"12345@example.org"@host.example.com>
Message-Id: <12345@[123@456]>
Message-Id: <"12345@example.org"@[123@456]>}}}
This particular usage, however, is not currently covered by this rule and is not known to be ''in the wild''.

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