Oh man it's good to read that it's probably not just the one connection I was trying to get fixed this afternoon. In this case it was Apple's Mail program that showed the initial symptom, but later I noticed the whole verizon.net zone didn't seem to work right.
I spent nearly 1/2 hr at a client's site seeing his mail come up as "Offline" when all the settings were set correctly, according to Verizon (FWIW).
I even tried to use a web browser to get to business.verizon.net. No luck with that either, although many other sites were working fine via the browser but not all (some reported server not found when they shouldn't have).
I think it turned out to be a DNS trouble. I think I temporarily added DNS's from MIT and then everything worked. I only got a few hrs sleep last night (trying to convert a database) so my feeble brain's a little fried.
Now's as good a time as any for me to go double-check that things are working. I'll remote in to his machine and report back...
[edit] Yup, things are still working there via Verizon business DSL with the supplemental non-Verizon DNS's added. (I have Comcast) That reminds me. A friend of mine phoned me the night before last asking if my Comcast was down like his. Turned out Comcast's DNS's were down then. Maybe something bad's going around to DNS boxes in general lately.