Gmail removes "position:relative" as inline CSS (Email Template)

Sadly, I suspect you may have to abandon your perfectly reasonable ideas of divs and positioning when designing for email. CSS support in email clients is a tangled nightmare.

The only (relatively) surefire way of forcing layout on email is to go with an old school tables layout, which is unfortunate, but unavoidable.

Campaign Monitor has an excellent summary of email client CSS support here.

I experienced similar layout problems when sending email newsletters. The solution was to use tables to position things properly. It's dated, but I think it was the only way to make things look the way they should.