since there are few issues with antispam for POP3, I suggest to skip this feature. The following is a guideline for the Last Astaro release 5.011:
A) Under Proxies: Enable SMTP Proxy
-> Under Incoming mail Section add the domains for which you want to relay and where to deliver the mail, Domains not contained here, will be refused.
-> Enable "recipient verification" so that email will be accepted only for valid existing users. (if this is not checked ASL will not check if a user exists and will accept all messages that will then appear, undelivered, under the proxy content manager menu)
-> Under Outgoing Mail section add your INTERNAL Network if you want the people to be able to relay
-> Leave Sender Address Verification disabled, because Sometimes you will receive emails from unexisting users (like online shops or mailing list, the reply address doesn't exists)
-> Enable Realtime blackhole list (Action Reject)
-> Enable spam Protection: I use the standard settings: 05 Quarantine / 08 reject
After this few steps don't forget to modify your MX record to point to your ASL box... if not done already.
