Joined: Tue Mar 23, 2010 9:48 am Posts: 42
We are running a small ISP i want to block spamming from my customers due to virus or any other issue to hit my upstream provider. I want to drop all the spam at my router itself without reaching my upstream provider router.
Other than blocking port 25/TCP for anything other than your SMTP server (if you run one) there isn't anything you can do on the RouterOS box itself. If you have your own mail server then you can use one of the many anti-spam engines (commercial or free) to filter out spam and other malicious emails.
Yes - as has been said by myself and mrz - block 25/TCP (SMTP) for all except your mail server. Your clients will then have to relay their email through your mail server, where you can apply filtering.
With this set of rules, a /32 (single client) is allowed to have up to 10 connections to port 25 at a time, and can send up to 35 packets a second over port 25. Once these limits are violated, they are blocked from sending more mail for 1 hour. Adjust to your needs.
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