IP blacklists for email servers

Mail servers need two different protections. Spam filtering works best with dedicated mail reputation lists and content checks. An attack blacklist such as isipsafe helps most with password guessing and probing against SMTP and IMAP.

Where isipsafe fits

• Block login attacks. Load the blacklist into your firewall with ipset or nftables to reduce attacks on mail ports.
• Report what you see. Postfix and Dovecot guides show how to report failed logins.
• Add a signal to spam scoring. With Rspamd, a listed sender can raise a message's score rather than being rejected outright.

What it does not replace

isipsafe is not a dedicated mail reputation system. For spam, combine it with a specialist list such as Spamhaus and a filter that also considers SPF, DKIM, DMARC and content.

Avoid losing real mail

• Prefer scoring over rejection for lower-confidence signals.
• Watch what gets blocked, particularly at first.
• Allow trusted senders and your own systems explicitly.

If your own mail server is listed

Check for a compromised account or server, then request removal from the list concerned. Correct reverse DNS and SPF, DKIM and DMARC records also help deliverability.