I've been blacklisted, how do I block port 25 for everyone except the mail server?

If you suspect that your Public IP is blacklisted because one of the workstations are spamming or creating too many outbound connections. With the help of Firewall access rules you can block all SMTP traffic from your LAN network to the WAN (Internet) except your MailServer.

Go to Firewall | Access rules (LAN to WAN) and create 2 access rules.

Step 1.  One to allow the mail server to send mail
Step 2.  One to block all outbound mail

1.  Allowing only the mail server to send mail.

Action: Allow From Zone: LAN To Zone: WAN Service: SMTP (Send E-Mail) Source: MailServer Destination: Any Users Allowed: All Schedule: Always on Comment:  Enable Logging: checked Allow Fragmented Packets: Checked

2. Block all other outbound mail on the network.

Action: Deny From Zone: LAN To Zone: WAN Service: SMTP (Send E-Mail) Source: Any Destination: Any Users Allowed: All Schedule: Always on Comment:  Enable Logging: checked Allow Fragmented Packets: Checked

NOTE: Ensure that rule 1 (Allow) gets higher priority than rule 2 (Deny).