I'm experiencing the same difficulty this morning and contacted support. Yesterday all my webmail was working great. Now, no matter which domain webmail I try I get "Server not found".
One good thing though, the regular email seems to work fine. I just came in here to see if anyone else was experiencing this problem.
UPDATE: This afternoon (3:30pm) Squirrel mail seems to be working alright. This is really good. Squirrel mail for nuts, when I have 3 domains that have something to do with nuts.. heartnutgrowers.com, besthearnuts.com and northernnutgrowers.com LOL Sometimes you feel like a nut...
well, anyway, just wanted to update this info
http://vernsdidj.com didgeridoo info and more