4. Sending mail from inside Oxford

This section relates to sending mail from inside Oxford to oxmail in its smarthost role. This should be done by MTAs. MUAs should use the message submission service.

Connection

ICTC Regulations require hosts to be registered in the DNS. Hosts that are not are denied service.

HELO/EHLO

Mail transactions must start with HELO.

Since all Oxford IPs must be registered in the .ox.ac.uk domain, the HELO argument must end in .ox.ac.uk . This is effective protection against compromised hosts running ratware which forges the HELO.

MAIL FROM

Although there is no restriction on the sender address, if it isn't valid then you won't know about delivery errors and may fail the recipients' sender address checks.

RCPT TO

The maximum number of recipients allowed for one message is 500. Excess recipients are temporarily rejected.

DATA

The maximum message size is 100 Mbytes.

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