[Mailman-Users] Mail not being delivered and consultants wanted?

[Anne Shroeder]

We've recently had multiple problems with our mailman installation
(currently hosted externally but hopefully soon to be moved in house) and
the most recent one is that mail is simply not delivered - most of the time.
Some messages seem to get through, but most do not.  Because I don't have
access to the server, I have to rely on the consultant who runs it to track
things down and he is not available 24/7 and when I'm getting yelled at by
my boss. 

My questions:  
(1) Is there a common cause for mail to disappear into the ether
(2) Are there companies or teams of consultants who do provide 24/7 support
for mailman installations?  

Anne