Email recommendations

[tech at nano.net]

I get a LOT of corrupt mailboxes. Just 187 mailboxes and daily problems. 
It's always the same error in the log files: "-ERR Unable to process From 
lines (envelopes), change recognition modes."

I've done some research and don't know any more about where the problem 
lives than I did before. I know that some From: lines are missing the 
colon, but I don't know why. Can anyone recommend a more forgiving popper 
or MTA? I'm running QPOP 2.53 and Sendmail 8.13.6.