Better spam filtering

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Dilbert
Posts: 27
Joined: Fri Sep 23, 2005 9:13 pm

Better spam filtering

Post by Dilbert » Sun Oct 23, 2005 10:36 am

Hi,
one big thing is missing in the MailEnable Enterprise Edition. The integration of a good spam filter like SpamAssassin. OK, I can integrate SpamAssassin using an MTA pickup event but what I want is:
  • Easy integration as you already did with the AV-scanners
  • Less resource utilization (the MTA pickup event needs 2 seperate processes - 1 for the pickup event and 1 for SpamAssassin)
  • Availablity of the spam filtering per postoffice/mailbox with global settings. I want my customers to pay for this service
  • You should add a rating system to the message filter (e.g. mails with SPF soft fail: 0.5 points, mails with viagra in message body: 5 points, ...) and then apply a filter to all messages with more than x points.
I'm currently evaluating MailEnable and other mail servers. If you would implement this within the next 3 months, I think I will buy MailEnable Enterprise. I think that spam and virus filtering are the most important features a good MTA needs.

Dilbert

fmaxwell
Posts: 151
Joined: Sat Aug 03, 2002 9:10 am

Re: Better spam filtering

Post by fmaxwell » Sat Nov 05, 2005 4:44 pm

Dilbert wrote:one big thing is missing in the MailEnable Enterprise Edition. The integration of a good spam filter like SpamAssassin.
That's a very bad spam filter because it is applied after the spam is received and it has already wasted your bandwidth. The idea when fighting spam is to block it so that your mail server does not accept it. That's why things like blacklists, SPF, and domain existence verification are the right way to go.
Dilbert wrote:Availablity of the spam filtering per postoffice/mailbox with global settings. I want my customers to pay for this service
Now I understand why you don't want to block the spam at connect time. You view spam as providing you with a potential revenue stream.

atinoco
Posts: 19
Joined: Tue Jun 21, 2005 4:56 pm

Post by atinoco » Fri Jan 06, 2006 7:56 pm

How do you verify the domain existence with ME Pro?

I get many spam messages with bogus from addresses like "great offer" or "great.offer", this check would help me get rid of them.

Thanks in Advance
-Andres Tinoco
PuntoWEB de Venezuela C.A.

fmaxwell
Posts: 151
Joined: Sat Aug 03, 2002 9:10 am

Post by fmaxwell » Fri Jan 06, 2006 8:10 pm

atinoco wrote:How do you verify the domain existence with ME Pro?

I get many spam messages with bogus from addresses like "great offer" or "great.offer", this check would help me get rid of them.
There is a tab called "Security" in the SMTP connector properties. Under that tab, the option that you want is called "Reject mail if sender address is from an invalid domain." Check that, and spam like you describe should be filtered out.

From the MailEnable documentation:

"When a user is sending mail to MailEnable, this option will check the From address in order to verify the domain it is coming from. This setting is used to stop people from abusing the mail server by using incorrect information. The majority of people who use an incorrect From address are spammers. This may affect valid email from incorrectly configured clients, so you should monitor your logs more often."

Dilbert
Posts: 27
Joined: Fri Sep 23, 2005 9:13 pm

Re: Better spam filtering

Post by Dilbert » Sun Jan 08, 2006 8:05 pm

fmaxwell wrote:That's a very bad spam filter because it is applied after the spam is received and it has already wasted your bandwidth. The idea when fighting spam is to block it so that your mail server does not accept it. That's why things like blacklists, SPF, and domain existence verification are the right way to go.
I would prefer this way of spam filtering but even with RBLs, SPF and so on, I can only catch round about 80% of the spam mails. Some domains implement SPF and don't list all email servers they are using, so I can't block SPF at the SMTP level.

It would be nice to have something like SpamAssassin, so I can say SPF fail 4 points, SORBS RBL entry 4.5 points and so on. If the mail gets more than 5 points, block the sender.

The same is the "Require PTR DNS entry" feature. Not all email senders have a correct DNS PTR entry for their MX. So it would be nice to have a rule "missing DNS PTR = 3 points". Something like GeoIP would be nice since most spam emails come from the USA and I don't get many emails from there so I would like to have a rule "mail from USA = 1 point".

OK, this is very much for a small email server, but a simple plugin system would be very nice. I'm an experienced VB6 developer, so I don't have problems writing my own filtering system. Maybe there are other developers interested in developing third party filtering systems (like MEFilter).

- Dilbert -

Dilbert
Posts: 27
Joined: Fri Sep 23, 2005 9:13 pm

Re: Better spam filtering

Post by Dilbert » Sun Jan 08, 2006 8:12 pm

Dilbert wrote:It would be nice to have something like SpamAssassin, so I can say SPF fail 4 points, SORBS RBL entry 4.5 points and so on. If the mail gets more than 5 points, block the sender.
What I forgot, I'm currently using SpamAssassin in an MTA Pickup Event (integrated using an ActiveX-DLL written in VB6). The SURBL feature of SpamAssassin is very nice. Take a look at http://www.inter7.com/?page=simscan. This is a program that integrates in qmail-smtpd and rejects spam during the SMTP transaction. OK, the spammer has to deliver the complete message but because I'm rejecting the email, I don't have to look at the quarantine every day to check it for false positives because the sender would receive an SMTP error message and is responsible to deliver the email.

- Dilbert -

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