When emails are sent, email clients have rules they apply before the email gets to your inbox. Sometimes they end up in your 'spam' or 'other' folders instead of your inbox. This is typically caused by words in the content or a link to somewhere, or a combination of those. The email client finds something that causes the email to be suspect in some way.
To fix the issue:
- Copy the email in Email+
- Delete a paragraph (or some portion of the content)
- Send a test email
- If the test email is still not delivered to the inbox go back to step 2
- When the email arrives in the inbox you must then figure out what you just deleted that was causing the problem. Sometimes you will need to go sentence by sentence, sometimes it is even more granular.
We don't know of an easier way to debug the issue. It doesn't take much time, it is just tedious.