If you are receiving bounceback messages or tags that your messages are being marked as spam and causing deliverabilty issues then you can use a mail-tester such as http://www.mail-tester.com/ to determine why your messages are being marked as spam.
You will be asked to send an email to a randomly generated email address that they provide you. Once you send the messages, click on the "Then Check Your Score" link on the main homepage. You will then receive a score based on a 10-point grading system.
You will also have the chance to review the following:
- Original message with full text and source headers
- SpamAssassin assement on the score of your message as well as ways you can improve deliverability such as adding a DKIM or SPF record
- Review of Authentication methods
- Notices of ways you can improve your messages such as the formatting or content of the messages
- Lists of RBL's your IP address is in
Each one of these sections can be expanded with the (+) next to each subject.