Hello Ron, 

POP3 is a pretty straightforward protocol. I would start by reviewing your POP logs for any obvious errors.

First make sure that the POP logs are set to detailed ( below ). If they are not set to detailed adjust them and then wait for the issue to happen again as the logs are not retro active.  

Next just do a generic search to see if there are any obvious errors. 

For the POP settings on the devices do you have "Leave a copy on teh server" enabled? If so you can try removing and readding the account. If this is not enabled you will want to skip this step as you will loose any emails not backed up. 

Thank you

Lisa,

The option to leave messages on the server when using POP will depend on the client/device you are using. That is not a setting within SmarterMail. Check your account settings in your mail client/device for this option.