Help Disappearing e-mails on EVO

I have started to have e-mails disappear on my HTC EVO. I've exhaustively looked at the settings on the EVO and in Outlook. Those appear to be okay; although I'm not certain. I also suspect perhaps a setting in Mailwasher Pro could be involved.The e-mails on the EVO seem to go away after I have successfully downloaded and viewed in Outlook and on the handheld. They disappear on the EVO after I then mark, and execute, all e-mails for deletion in Mailwasher.

By the way, this started happening after I installed K-9 e-mail client on the EVO. However, I have gone back to using the standard EVO e-mail program. Having same problem with both programs. Wondering if maybe I should uninstall K-9.

One test I did was to send an e-mail from one of my pop accounts to my gmail account. I allowed it to pass through Mailwasher ...downloaded and viewed it in Gmail on PC. Then, marked it for deletion in Mailwasher...ran it through....and it disappeared in Gmail on PC.

Any ideas?