I'm sure you've all seen the many 'email washer' type programs that change free to f.ree and money to mon.ey. However, if you are sending mail out from your own server then it may well be that you aren't aware of some other problems that can cause your email to be bounced OR silently dropped by other mail servers. There seems to be a lot of attention paid to the content of emails and little or no attention to the other areas that can cause mail delivery failures.
Here is a short list of things you can do to improve email delivery. These are issues that I've had to deal with myself during my 12 years as an ISP. Note that these points are mainly aimed at those of you with your own dedicated servers. If you are on a shared server then you won't have quite as much control ... though the DNS and script related points are still relevant. Also note that not all mail servers implement the measures that I will be discussing - but there are some that do, so several problems with your DNS or mail server configuration can lead to a considerable number of undelivered messages.
1. Reverse DNS - The server that sends your mail should have a corresponding reverse entry. What that means is that if your server hostname is mail.mydomain.com and your DNS server says that this address is IP 1.2.3.4, then there should be a corresponding 'reverse' entry saying that 1.2.3.4 is mail.mydomain.com. Some mail servers will check this before accepting your mail, and reject your email if these DNS entries don't match. This can be fixed by adding the appropriate entry or in some cases asking your host to add an entry (which most will gladly do).
2. Checking the Sender - Some mail servers will now check for a valid sender. How this works, is that when you send an email, the receipient's server will immediately connect back to your server and start a 'conversation' with that server as if it is going to deliver mail. If your server says that the sender is 'User Unknown' or there is some other type of error then the delivery will fail. Always use a valid address on your emails ... even if it means creating a 'donotreply@yourdomain.com' mailbox that you rarely look at.
3. Postmaster@, Abuse@ - You've probably seen these mentioned and heard that you should have them ... but do you have these addresses for all your domains? These addresses are sometimes checked by anti-spam services when someone submits a spam report. If you don't have those addresses then you can end up on the 'rfcignorant' blacklist. Granted, only the most anal of ISPs and businesses use that blacklist, but how serious are you about getting all of your email delivered? No point in taking chances. Things like this can also add to the 'score' an anti-spam program will give your message and edge you closer to the threshold it sets for rejecting messages.
4. Script-based mailers - If you are running a membership site, chances are it is written in PHP or Perl. In this case it is the mail headers that you need to be wary of. Anti-spam applications like SpamAssassin, which is very popular, examine the headers and give your message a 'score' based on many factors including how valid the headers appear. It is outside of the scope of this article to go into details, but if you have a programmer on hand, ask him to check any script-based mailers you have and see if he can add or change some of the message headers.
5. SPF - SPF has been around a while now. It is gradually being adopted by more and more ISPs and businesses but is by no means a cause for concern - yet. It can prevent people from forging your email address though, at least for the servers that use it. How it works is that a record is added to your DNS stating which server IP numbers are allowed to send mail from your domain. So ... if SPF says that mail from you should be coming from IP 1.2.3.4 and Joe Spammer tries to send mail from IP 4.3.2.1 with a return address of you@yourdomain.com, any server that is using SPF will reject that mail.
I strongly suggest that you visit dnsreport.com and put your domain in there (just the domain .. without the 'www'). This will give you a quick look at whether you have any glaring DNS or mail issues. If you see any red in there then you need to get it fixed. If you see any yellow, then you should have someone take a look to see if there are any issues serious enough that they should be resolved.
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Gary Smith has been an IT Consultant and ISP for 12 years and a software developer for 25 years. His small business, SOHO Internet Consulting, offers IT and marketing services to other small and home based Internet businesses.
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