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So I am fairly new with SmarterMail I had always used Exchange. I recently found out my domain had been blacklisted for sending out excessive SPAM. I discovered one of our email addresses had send out THOUSANDS of messages of SPAM. I immediately changed the password for the account but I am thinking security is not right on this server that allowed this person to use my SMTP server to send these messages.
So is this the best pracrtice for security using what I have available to me?
I installed an SSL certificate and under BINDINGS I have all ports changed to SSL EXCEPT for port 25 SMTP. (I do have 465 SSL SMTP as well). But I kept port 25 there because isn't that required to receive mail?
Also in my firewall I have NAT set up and the only traffic I allow in from the outside are 25, 443, 465, 587, 993, and 995.
I feel like having port 25 open is what caused this to happen but don't I need it for the MX record and to receive mail from the outside?
Any other tips?