How does MSN filter spam?

Question

I am trying to create a newsletter for our business.

The last few days have been spent testing, and one of things I have noticed is that MSN seemingly randomly filters out some of my test messages.

This is super-frustrating.

I like the PEAR Mail MIME-package, and have been using that. I may send one email from one of our servers, resulting in the message getting through, and in the next minute, the same message sent from our other server ends up in the junk folder. Then if I add an attachment to the email, and the same message passes though the filter from the server that was previously blocked. I think. What the ####? Is this like throwing a dice, without me having any control over what is trash, and what isn't?

I have sent email from several servers, all of which are shared. But I am unsure this is the problem. The problem is that it is seemingly random how MSN filters email. Some emails get through, and some other don't for seemingly irrational reasons.

I am running out of ideas, but I am not giving up. Therefore I am writing to you for HARDCORE technical info on how MSN filters spam.

Answer 1

First of all, this is probably better suited for ServerFault. The problem is more infrastructure related than application related.

This is a common problem and isn't completely solvable especially if you are using shared mail servers. But there are things you can do to increase the likelihood that your mail will be accepted by mail services.

• Run your own mail server, do not use a shared server. This way you will have better control over the mail server's reputation. Mail server reputation is important, as others using the server can cause its reputation to drop, which makes your mail to be less likely to be accepted. The important thing is to have your own dedicated IP number.
• Make sure you have reverse DNS set up for your mail server. Not having reverse DNS properly configured is a great way to have your mail rejected.
• Use SPF, SenderId, DomainKeys, and DKIM. I believe MSN uses SenderId. These provide you with a way to tell the other mail server that the sending mail server is an approved server for sending mail from your domain name. If these pass, then the mail is much less likely to be spam. Here is an article on these things: http://www.digitalsanctuary.com/tech-blog/debian/setting-up-spf-senderid-domain-keys-and-dkim.html
• Don't send spam! If you do all these things and still send spam, you'll still have troubles.
• Monitor for bounces, possibly using VERP.
• Make sure to provide a means to opt-out of your list.

Additional advice can be found here: http://serverfault.com/questions/48428/how-to-send-emails-and-avoid-them-being-classified-as-spam

Here's an example of the SPF configuration I use: http://serverfault.com/questions/122121/dns-zone-file-spf-configuration-to-support-sending-mail-from-multiple-servers-and

Newsletters especially can easily look like spam. You might consider using a service like MailChimp or similar that specializes in email marketing and mass emailing. They will make sure to tend to all the technical details, remove their servers from blocklists if they get blocked, and so forth. They also provide you with opt-out features, CAN-SPAM compliance, and more.

I've found the Spamtacular blog to have good information as well (it looks like they are having some technical issue right now - hopefully it will be online when you view this).