OK more information:

These numbers, of course vary. Below are the ranges:
when the spam filter stops working 

how many messages are in the in box?     5-50

How many messages are in the spam folder?  10-500

how long has pmail been up?  1  - 12 hours 

How often is it failing?  1-5 times daily

I work for a man (mostly light computer work) who has been using pegasus for ten years I've been working for him and his web business.  I mention this in case the amount of email could be a factor. Most email is saved.  unless there is an attachment, then the attachment is saved to the pc, then deleted.  the pmail folder is 1.5G of mostly text file email. Pegasus is up 24/7. Recently the spam filter has mysteriously just stopped working in the middle of the day.  Thinking it possibly was just 'stuck' because of the volume of email he gets (about 2000 every day) we did an email purge. Basically created a new profile called 'old' copied the his profile into that so if he needs to search for something he can just switch profiles and do the search. That went smoothly and I deleted everything that he doesn't use all the time.  That knocked the folder down to 128M.  The really nice thing is it doesn't take near as long for pmail to load the profile, unfortuneatly it didn't solve the stopping spam filter problem. Not that I had high hopes that it would.  Is there anything that I can look for or reset? (aside from the computer itself.) 

How many messages are in the "New Mail" folder?  If there are too many, Pegasus Mail stops checking for new mail.

between 5 - 50 at any given time of the day.  That is just messages that are not spam.  When the spam filter stops working, all the spam goes in there too and it gets filled real quick if he isn't at the desk to restart. Though that does make me wonder  how many are in the spam folder at that time.  I'll check on that info.

Thank you.