Take Away: We all know that many, many emails are regularly blocked by various anti-spam mechanisms.
This is a good thing - considering all the spam being generated.
Here are some tips for helping your messages get to your intended recipients.
Observing a few techniques will help ensure your messages, sent via psSendMail v2, will make it past the spam filters.
1) One of the first, and most conisstent things examined by spam filters is the "X-Mailer" line in email headers. This line is intended to identify the program that originated the messages. Many, many programs designed to assist spammers have been identified by their X-Mailer signature, and are summarily blocked.
With psSendMail v2, you have complete control over your X-Mailer header, and we strongly urge you to use it. Select a unique, descriptive value for your program.
Furthermore, if you market your program to others, you should craft a mechanism that gives each of your customers a unique X-Mailer signature. Why? Because if one of your customers uses your program for spamming, you don't want the rest of your customers punished.
Note: A missing X-Mailer header line does not constitute an invalid message, but it ought to make anybody suspicious. Even if you don't provide your own value, psSendMail will construct one for you. Don't let it. Specify your own.
2) Don't engage in spamming! A unique X-Mailer is no protection against being flagged as a spammer, and the best way to get flagged is to do it - spam. The consequences can be severe: Your ISP could suddenly find all messages originating from his domain blocked! That, or course, will infuriate his other customers, and you shouldn't be surprised if he comes down hard on you.
3) Be careful of your message content. Experiment with several different spam-blocking programs and services, studying the kinds of messages that are landing in your junk or spam folder. Offering Valium, Vicodin, Soma, Rolex watches, or body part enhancement products may be all it takes to trigger some spam filters.
4) Use a "real" ISP. Many spammers rely on the ease of obtaining free email accounts to rapidly change their email addresses and avoid being "logged" as spammers. Or, if they are, they hope a new account will allow them to continue spamming.
Some spam blockers using heuristic algorithms, may go to work if your address ends in Hotmail, Yahoo, Gmail, etc. Those domains, alone, may not result in blockage, but found in combination with other factors, they certainly might.
5) Send emails only to willing recipients. This is just common courtesy, common sense. Many good spam-blocking programs allow their users to report spammers. Trust me, they will. I report spammers gleefully; I hate the scumbags.
Yes, the law allows you to pump out emails to people you've done business with. My advice is to ask people for the privilege of emailing them. As a further courtesy, don't make them "opt out," make it easy and attractive for them to opt in. And, always, always, make it clear and easy - in every email - for recipients to change their minds and opt out.
6) Email sparingly. It's so easy to amass a database of customer email addresses that it's tempting to email them daily. I call that punishing the customer for being a customer. How much sense does that make?