Spam Filtering

The mail server tries to filter out spam by default. Obvious spam will be rejected. Probable spam will be placed in a mail folder called "Junk." You should check the Junk folder periodically to ensure that legitimate emails haven't been inadvertently filed there. There's no need to empty the Junk folder; messages older than 30 days will be automatically deleted.

Auto-Learning

If you find spam in your Inbox, move it to your Junk folder and the system will learn to recognize it as spam. Similarly, if you find legitimate mail in your Junk folder, move it to your Inbox (or any other folder), and the system will learn to recognize it as non-spam.

Mail Filtering

The mail server also supports sieve as a mechanism for server-side mail filtering. This will allow you to set up auto-replies, sort incoming messages into folders based on sender/recipient/subject, and other related capabilities. Generally this functionality will be implemented in your mail client.

Webmail

The webmail systems have mail-filtering capability, and those rules are set up on the server. That means that if you set up a rule within (for example) Roundcube, it will run on the server at all times, whether you're logged into Roundcube or not.

Thunderbird

Thunderbird supports sieve filters using the Sieve add-on.