Why declare viewport in html email campaign?
The majority of HTML emails and boilerplate that I've seen coded by other people, always declare a viewport meta tag.
I mindfully always avoid declaring a viewport and strive for a very high level of cross/backwards compatibility.
Declaring viewport settings render the email totally unusable for any of your audience using a Blackberry and overall is very poorly supported by any client.
Is there a reason to use this tag that I missed? Why are the majority of other peoples emails I see using this?
Additional Reference: http://www.emailonacid.com/blog/details/C13/emailology_viewport_metatag_rendered_unusable
Answer
If you want blackberry to work then by all means do not declare your viewport tag. Also don't nest tables, that will break the layout on blackberry too.
however, your other (vast majority of) mobile users will suffer. They will be able to pinch and zoom which can break your layout, I've also heard of resizing issues on high ppi screens without viewport, and I've had problems with horizontal scroll bars on my emails when I tried to go without it as well.
My current client has a huge email list. I forget the precise open stats, but versus the iphone and android's 100-140k opens each, blackberry opens accounted for 400.
of course one of their higher ups (above our contact for them) was the guy that just would not get rid of his ancient rolly ball blackberry and was pretty upset that he wasn't seeing anything. It took a while for us to convince them that dropping legacy blackberry support was the right move.