Active rule currently published.
This rule detects multiple login failures to the Courier IMAP and POP3 servers from the same IP. The intent of this rule is to detect a malicious party attempting to brute force guess passwords.
The default settings are to detect 6 login failures, from the same IP, within 60 seconds.
This rule does not shun by default, it only alerts.
This rule can be falsely triggered if multiple users are using the same IP address, such as behind a firewall and multiple users generate 6 or more failures within a 60 second period.
This can happen either with a large number of users (less probable), or an email client that can generate multiple connections at the same time (as with the IMAPX protocol, which is more probable), however because there are other rules that detect faster denail rates its very unlikely a single client would generate failures at such a slow rate.
If you believe that this is a false positive, then disable this rule or whitelist the source IP.