I was looking through the results of our secret shopper study this week and came across this interesting tidbit. Of the schools in the study this year, 15% were also in the study in 2013 - but that's the boring part.
What is most interesting, though, is that over half of them were using some of the exact same emails in 2013 - no graphics changes, no subject line changes, no content changes. In fact, the only change in those emails was the name of the enrollment/admission counselor. 
Oops! Not a good sign that these schools have a very solid understanding of what is working and what isn't.
Sure, it could mean they found some messages that were working. But remember this: I read those emails, and I can tell you that bland doesn't work - at least not anymore in higher education email marketing.
You don't need to be changing your emails monthly, but you should be updating them routinely. Test the ones that work best. Find optimal days/times to send messages. Compare response rates for each of your programs and by audience or student personas.
We are in a world, and in an industry, at a time when every single new student counts. I've not met an admissions or enrollment management professional in graduate and adult education that has told me she/he does not need or want anymore new students.
If you're feeling the pressure, and wonder what else you can do - then look at the automated emails you send. Are they updated? Are they performing the way they should? Do they include best practices?
Would this checklist help?