RBL is an abbreviation for "Real-time Blackhole List" , a list of IP addresses whose owners refuse to stop the proliferation of spam. The RBL usually lists server IP addresses from ISPs whose customers are responsible for the SPAM and from ISPs whose servers are hijacked for SPAM relay.How does it work ? If you receive an email from a blacklisted ip address (listed on RBL) the email will be rejected. RBL permits to reduce your inbox SPAM by 30% or more.

The Bayesian filter stops SPAM at the SMTP server. The Bayesian filter is adaptive to new spam and requires no operator intervention after the initial setup phase. It permits to indentify about 60% of your SPAM messages. You can report false positive/negative using the using the Bayesian filter Email interface (please read the documentation) .

The HELO filter REJECTS email messages which do not validate Format of HELO (rfc4408).We reccomend to enable this filter to reduce received spam.

The SPF filter REJECTS email messages which do not validate Format of SPF . SPF fights return-path address forgery and makes it easier to identify spoofs.Domain owners identify sending mail servers in DNS. SMTP receivers verify the envelope sender address against this information, and can distinguish authentic messages from forgeries before any message data is transmitted.We reccomend to enable this filter to reduce received spam. To reduce risk to filter valid email , soft SPF failures will be accepted.

The PTR filter REJECTS email messages from senders with an invalid or missing PTR record (Click here for more details ). A PTR record or pointer record maps an IP address to the canonical name for that host. We reccomend to enable this filter to reduce spam.

The MX/A filter REJECTS email messages from senders without a valid MX or A record (Click here for more details ).An MX record or mail exchange record maps a domain name to a list of mail exchange servers for that domain. An A record or address record maps a hostname to a 32-bit IPv4 address. We reccomend to enable this filter to reduce spam.

The Bomb Regular Expression filter (bombRe) is a spam blocking mechanism based on Regular Expressions. If there is a match to either of these Regular Expressions the message will be blocked (REJECTED) from delivery . It's a very powerful mechanisms for rejecting spam, but it can also be problematic by causing false-positive matches and mistakenly blocking email . So check your BombRe log page often if you activate this filter.

URIBL lists domains (url) that appear in spam, not where they were sent from.  If you receive an email containing a domain (url) listed on at least 1 of the following uribl providers the email will be rejected (and logged) 
multi.uribl.com, sc.surbl.org, ws.surbl.org, ob.surbl.org, ab.surbl.org, ph.surbl.org, jp.surbl.org .

Delaying is a new method of blocking significant amounts of spam at the mailserver level, but without resorting to heavyweight statistical analysis or other heuristical approaches .This method is also called  "Greylisting". If you wish to know how works this filter please read this page and our documentation here .

The Penalty Box filter blocks mail based on the IP and the history of this IP. The history is written to a Black Box database by scoring all events (Bayes, Delaying, missing MX/A, RBL, URIBL, BombRe, Helo, PTR, spf, and some other server wide filter), also if you have 1 or more filters disabled.. If the score per specified time interval surpasses the threshold the mail is rejected (and the IP is marked for blocking). These IPs continue to get score values up to the "Extreme Threshold". After that the IP is denied the connection in a very early stage.

If you enable this filter you permit your mailserver to receive email only to existent email addresses on your accounts (forwarders included)   stopping every email spam dictionary attack.  The sender which sends an email to a not existent email on your account (i.e. random_word@yourdomain.tld ) will receive following error :  550 5.1.1 User unknown: random_word@yourdomain.tld .
NOTE : If you enable this filter you lose "email domain forwarding" and the "default address" features.

Virus email protection is enabled by default on all your domain names.