I was just searching around and I found that, according to this what-to-know-about-html-emails link that HTML emails have no standards.
In this how-to link, it describes some of the missing standards, such as padding
for div
s and p
s but the support for table
s. It also recommended to use HTML attributes whenever possible because of the sporadically-supported CSS.
This was my problem: I used some unsupported CSS.
I hope this helps someone!