[thelist] Double Emails continued in PHP

[Jay Blanchard]

[snip]
Ok. As a quick recap... 

I'm sending email with PHP and using only one mail() function call. When
I
send this email, sent to my hotmail account, I receive 2 emails with one
call. When I send this email to my outlook account, I only receive 1
email. 

Anybody have an idea what's going on here?
[/snip]

Can we see some code?