After setting up MiaB, I left all the posts open on my firewall, since the documentation mentions that MiaB has it’s own firewall.
For my own piece of mind though, I want to block the ports that are not necessary on my firewall also.
As per the documentation the following ports must be open:
22 (SSH), 25 (SMTP), 53 (DNS; must be open for both tcp & udp), 80 (HTTP), 443 (HTTPS), 587 (SMTP submission), 993 (IMAP), 995 (POP) and 4190 (Sieve).
My only concern is port 22. I usually block that for everyone except my own WAN IP.
Does it really need to be open? Is SSH used for emails?