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The last post: Building your own mail server, part 2


Funny, OpenBSD provides a greylister, spamd. However, the article does not mention it.

Spamd can tar pit hosts on the blacklist. Blacklisted hosts are sent to a separate dummy SMTP server that responds slowly and discards everything. has details.

Thank you for including configuring submission protocol.

You neglected the "Why"

Many ISPs block outbound SMTP, but permit outbound submission protocol.

May I suggest a followup article.

Mail senders that do not play nice with greylisting.

There is a well loved advertising company that retries sends from EVERY host in their netblock.

There are several parcel carriers that attempt delivery only once.

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