Mail constantly indexing

[J Patrick Draine]

Friends, I need a bit of help. All my system software has the latest 
updates. Mail is getting hard to deal with because it seems to be 
indexing very very frequently. So when I want to delete a message and 
go to the next one to read it's too busy indexing to respond. Not all 
the time, but very frequently.
Now I do have many undeleted messages (over 3100, read but not thrown 
away). Is that the problem? Or are there certain settings which I can 
tweak to decrease the frequency of Mail's indexing?

Patrick