I am having terrible problems with sending emails via PHP to Hotmail and Yahoo. I am sending through PHPMailer which is supposed to make delivery more reliable. They keep ending up in the spam boxes.

It is software I am distributing so I have to make sure the emails will definitely send. I can't rely on whitelisting IP addresses or anything like that.

When I send the emails as plain text they end up in the Hotmail inbox and Yahoo spam box. Then all I did was change to sending them as html and guess what, they go to the Hotmail spam box and Yahoo inbox.

These are the things I have concentrated on that I have heard could make a difference:
  • Focus on not using "spammy" words
  • Sender email address is the same domain the email is being sent from
  • Proper return-path header

Does anybody have any advice for me?