@bmeeks:
@NollipfSense:
@bmeeks:
No, the POP3 preprocessor most definitely does not communicate with any mail server. It is simply looking at the commands flowing back and forth between email clients on your network and whatever mail servers they are connecting to (assuming that traffic passes through Snort). The line you underlined from the Snort manual is simply saying you need to tell the POP3 preprocessor what ports to be looking at within the incoming/outgoing datastream. It does not imply that Snort is talking to the mail server, though. Telling the POP3 decoder what port is in use lets it filter the traffic and only inspect data coming or going from the active POP3 port.
You define the POP3 ports on the VARIABLES tab for the interface in Snort. There are settings on that page for servers and ports. Leaving boxes blank will use the default values which are shown in the help text under each box.
Bill
Thank you Bill for the detail explanation. Well, one cannot just add the port…one has to create an alias; so, I created two firewall aliases, inmail and outmail and added firewall...see pic. Then, I added the aliases to Snort's variables tab > SMTP >outmail and POP3 >inmail. But, I cannot send or receive mails...should I have added anything in the server section? I got this Snort alert and have since changed the source port. Had to hide destination IP for privacy on Snort alert pic. Outmail port is 465 and inmail port is 995.
Port 995 is typically for POP3S (encrypted POP3), so Snort is going to have trouble seeing everything correctly on that port. That rule is a "false positive" in your case because it is looking at an SSL encrypted datastream, so the byte patterns are not going to match the "standards" that Snort would see on a port 110 plain-text POP3 connection. That's why the rule is triggering.
So short answer is just disable that rule as it is going to fire on you a bunch and means nothing on an encrypted session.
Bill
Thank you Bill…disabling the rule worked and can now send, received emails from my SOHO...in time for Monday morning!