Here's an easy way to improve results of your fundraising emails: Ask donors to do only one thing.
As the Emma Blog put it at How Choice Paradox is killing your email click rates, Emails with a single call to action (rather than several) can increase sales a whopping 1617%.
The choice paradox is this: While people like to have choices, choices can lead to indecision, which leads to the choice of none.
What that can mean in fundraising is when you ask donors to support the annual fund ... and give look into planned giving ... and register for the walk ... and support the capital campaign ...
They are more likely to give up entirely on all of them. And you lose.
The advantage of email is you can turn all those choices into one message each. In direct mail, that's probably not affordable. You have to choose the ones that are really worth spending your money on, and drop the rest from your lineup.