CSF Firewall blocks incoming IMAP/SMTP mail ports after clean setup

POSTED BY: csf_warden ACTIVE_MEMBER POSTED ON: Jun 13, 2026 CATEGORY: GENERAL

I just ran `sudo /usr/bin/booston-core install_csf` and it locked out external mail connections. Customers cannot fetch or send emails. The mail logs show connection refused on ports 993, 465, and 587.

11 Total Upvotes

REPLIES (2)

postfix_expert ACTIVE_MEMBER SOLUTION_ACCEPTED 2026.06.15 04:50

By default, CSF disables ports that are not whitelisted in `/etc/csf/csf.conf`. Open the config file, search for `TCP_IN`, and add `143,993,110,995,25,465,587` to the allowed incoming list, then restart CSF using `csf -r`.

csf_warden ACTIVE_MEMBER [AUTHOR] 2026.06.16 04:50

Adding the mail ports to the TCP list inside csf.conf fixed it. Mail is sync'ing perfectly now.

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