Running on Thunderbolt, K9 crashes, runs s-l-o-w....
What else can I do? Any fixes?
If it's POP3, consider using or making a GMail account and set it up so that your POP3 email can be fetched via GMail. It'll push messages to you more quickly, won't take up space on your phone like regular POP3, and you can set it up so that multiple accounts are fetched by the same email address.
How to do it: Use Gmail To Push All Your POP3 Email Accounts To Your Android Phone | GizmoFusion
K-9 doesn't usually work slowly and that's coming from someone who had it on two much slower phones. Hope this helps.
Old Phones: HTC Droid Eris, Droid Pro
Currently using: Droid 4