I am using the integral mail function to send email from one of my sites. When I debug while sending email, I see my function run only once. The function also echo's out the single distinct multipart identifier used in the one function call.
When the email arrives in my inbox, I have two copies. Same content. Except... The second email has a different multipart identifier. My function never generated the second identifier.
I am stumped. I have been searching and have made sure I am not doing something stupid like including a "To: " line in the header, I am not using CC: or BCC:.
Some google results indicated that a hosting companies spam filters can do things like this... The email is being delivered to my domain email, which is served by Google Mail.
Thanks for any help!