5. Sending mail from outside Oxford
This section relates to sending mail from outside Oxford to oxmail
in its mail exchanger role.
email@example.com bypasses most checks in order to allow
queries about problems.
The following DNSBLs are used
Mail coming from a server listed in one of these DNSBLs won't be
rejected. It will attract a weighting in the SpamAssassin scoring and
also experience small delays in response to some SMTP commands.
Mail transactions must start with HELO.
The HELO argument must be syntactically correct. See RFC1123 section
5.2.5 and RFC5321 section 184.108.40.206 for guidance on choosing your HELO
argument. A common mistake is to use the underscore character; this is
The envelope sender must be valid and accept error messages (aka
bounces). A common mistake is to send mail from a script without
thinking about the sender address e.g.
firstname.lastname@example.org . If there's neither an MX
record for nor an MTA on foo.example.com then the sender address will
No recipient local-part may contain any of the following characters
@ ! % / | "
The maximum number of recipients allowed for one message is 500.
Excess recipients are temporarily rejected.
The maximum message size is 100 Mbytes.
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