[Mailman-Users] Virtual hosts

Brad Knowles brad at shub-internet.org
Wed Apr 11 03:59:34 CEST 2007

At 10:13 AM -0700 4/10/07, Mark Sapiro wrote:

>>I believe that all this is documented in the FAQ.
>  It isn't AFAICT.

I thought it was, but I'll take your word for it.

>                   I was going to add it, but I am looking for a specific
>  RFC reference. I have looked at several RFCs and I don't see anything
>  that talks about rewriting domains in headers. All I found was RFC
>  1123 (STD 3), sec 5.2.2 which requires that canonical names, not
>  aliases, be used in MAIL and RCPT commands. Can you tell me where to
>  look?

RFC 1123 has been superceded.  For these things, look at RFC 2821, 
section 2.3.5:

2.3.5 Domain

    A domain (or domain name) consists of one or more dot-separated
    components.  These components ("labels" in DNS terminology [22]) are
    restricted for SMTP purposes to consist of a sequence of letters,
    digits, and hyphens drawn from the ASCII character set [1].  Domain
    names are used as names of hosts and of other entities in the domain
    name hierarchy.  For example, a domain may refer to an alias (label
    of a CNAME RR) or the label of Mail eXchanger records to be used to
    deliver mail instead of representing a host name.  See [22] and
    section 5 of this specification.

    The domain name, as described in this document and in [22], is the
    entire, fully-qualified name (often referred to as an "FQDN").  A
    domain name that is not in FQDN form is no more than a local alias.
    Local aliases MUST NOT appear in any SMTP transaction.

See also section 3.6:

3.6 Domains

    Only resolvable, fully-qualified, domain names (FQDNs) are permitted
    when domain names are used in SMTP.  In other words, names that can
    be resolved to MX RRs or A RRs (as discussed in section 5) are
    permitted, as are CNAME RRs whose targets can be resolved, in turn,
    to MX or A RRs.  Local nicknames or unqualified names MUST NOT be
    used.  There are two exceptions to the rule requiring FQDNs:

    -  The domain name given in the EHLO command MUST BE either a primary
       host name (a domain name that resolves to an A RR) or, if the host
       has no name, an address literal as described in section

    -  The reserved mailbox name "postmaster" may be used in a RCPT
       command without domain qualification (see section and
       MUST be accepted if so used.

I'm still looking for a specific reference from RFC 2822 that would 
be applicable to the case of the "From:" header.

Brad Knowles <brad at shub-internet.org>, Consultant & Author
LinkedIn Profile: <http://tinyurl.com/y8kpxu>
Slides from Invited Talks: <http://tinyurl.com/tj6q4>

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