In the past, I remember having to open port 25 for email servers to check back and verify that in fact, an email was sent from an email server.
Does this still pertain these days? If you have 10 outbound SMTP servers, should you have port 25 be open from www to them, so that external recipients can connect back on port 25?
If I remember correctly, spamassassin, had a feature to check this… however, not certain.
I haven’t heard of anyone doing this since maybe the 1990s. And it wasn’t really a good idea even then.
To catch up on modern spam prevention techniques, see Fighting Spam – What can I do as an: Email Administrator, Domain Owner, or User?
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