The A/B test is very helpful. But I'd like to request an option where users would have the option of testing two completely different campaigns. For example:
Group A: subject line A, content, A, from name A
Group B: subject line B, content, B, from name B
Personally, I don't think the results would be all that helpful because there'd still be only one measurement and there are too many variables. But I've had a few clients ask about it, for example because they want to insert their own tracking pixels to track two subject lines and currently they can't because the HTML content has to be the same for both subject line A and B, unless I'm missing something (which is quite possible).
Yeah, we keep it restricted to limit the variables, as the results probably wouldn't be helpful with that many variables, as you mentioned. Interesting about the tracking links, though! In this case, you'd need to set up separate campaigns altogether to add all the different variables and run it as a manual test.
Others have asked for the ability to test more than one variable, however, and I've added a vote for you.
Add a vote for me as well, but it can be simpler. The 2 most important metrics are open rate and click through rate.
Each variation (A & B) should get 1] a unique name/subject 2] unique content
Then the "winner" is the combination of which creates the most opens and most clicks.