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I would like to force users of a system to send email only using a submission port (such as 587) and then disable authentication on port 25 so I don't have users trying to authenticate using plain text.

What configuration changes would I need to make to disable authentication on 25 so users have to use a submission port to relay?

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up vote 3 down vote accepted

From the Exim manual (section 38.1). Hope this helps:

You can insist that any client that uses the AUTH command for authentication must start a TLS session first, by setting auth_over_tls_hosts. For example,

auth_over_tls_hosts = *

means that all authentication must take place over secure sessions. This setting does not force the matching hosts to use AUTH, but if they do, they must issue STARTTLS first. The availability of the AUTH command is advertised to such hosts only after a TLS session has been started.

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