10) SenderScore Certification
Microsoft's answer to a whitelist, getting SenderScore Certified is an often lengthy process and costs a decent amount of coin (depending on your volume). It was formerly known as Bonded Sending, where you have a pool of money that is substracted from with every complaint. If you follow the above guidelines, getting Certified should be fairly simple (but may take up to 90 days). This especially helps with Hotmail and other Microsoft products.
11) Mail Software Footprints
When using third-party software for managing your mail campaigns, always run tests and see what, if anything, they add to the header of a message. For example, many softwares like to place their "signature" into the header, typically as an X-Header: field. Some of these softwares, having been popular with spammers, draw red flags due to these signatures so turn them off when possible or research your software carefully before investing in it.
12) Open Relay
While most people are aware of this these days, by default, most mail agents allow open relaying and this is something you NEED to restrict. An open relay is a system that allows anyone to use it as an SMTP server for sending mail out; not just authorized users and addresses. Restricting it varies per mail software, but is generally quick and painless. Aside from the obvious problem of spammers finding and using your server, ruining your IP's reputation you worked so hard on keeping clean, ISPs can run a quick test to tell if you are "open" or not and if you are, they won't accept your mail in most cases.
13) Content / Filtering
Even if you pass all the above tests with flying colors, you still face a powerful foe; content filtering. This is more of a case-by-case issue, but I will attempt to give you a few tips.
First, know the major filtering softwares. For example, SpamAssassin is still a popular standard. Install them on your own if you have to and perform some trial and error, to determine the what words and email characteristics are heavy triggers and which don't carry much weight. Filter systems can check everything from "Do the domains in links in the email match the From: address?" to "what is the HTML/Text ratio versus images" along with weighing specific words, for example "viagra" is a commonly-blocked one.
Try and test your campaigns before sending them out for real, to get as low of a score as you can with different filtering systems. Again, this is a case-by-case basis factor and no one answer will magically get you through all filters.
One additional note: try and keep your HTML emails simple and clean (valid XHTML/CSS). Some ISPs are taking this into consideration.
There is still plenty more information on this topic, but the above points will hopefully have you understanding how to send emails out and how to reach your customers' inbox better than you currently do. Some industries, such as dating, rely on mail so much that a single day of being blocked can result in a conversion drop of up to 50%. The truth is, if your business relies heavily on email marketing, you should have someone dedicated to monitoring and fixing issues with your mail systems at least 2-3 hours per day.
Also, always remember that there are no guarantees in mailing. Unfortunately, due to abuse, some ISPs have become so tight that clients have a hard time receiving mail they want to receive! You may find yourself blocked for no apparent reason for a day or two, only to return to the inbox for another few months. Just do your best and you will see your deliverability increase.
If you have any specific questions, feel free to ask them in the thread below and I will answer them as best I can. I did not want to show any bias by recommending any particular monitoring or consulting services (as well as, I don't recommend anything I haven't used myself), but there are many out there who do genuinely know what they are doing. There are, of course, others who simply want your money and have no idea what they are doing.
I'll leave you with a handy tool, a method to easily test your SPF, Sender-ID, DomainKeys, DKIM and SpamAssassin score:
Send a test email out (ideally with the content you actually intend to send and from the real mailserver) to [email protected]
and within minutes, they will reply to the From: address in your email with a report. Enjoy!
ABOUT THE AUTHOR
Varius (Keith) is best known around here for his many years in the adult dating space, being a part-owner of IwantU. He has regularly sent out millions of emails a day and spent a large amount of time understanding how to reach customers' inboxes. He currently is involved in multiple partnerships involving Adult, Gaming and Mainstream projects.