Trashed message in IMAP account reappear in Inbox

I have this problem on both an iMac and a MacBookPro. Both with same version of Outlook and running MacOS10.7.5

When I delete messages from the Inbox they go away but reappear a few seconds/minutes later. This only happens with an IMAP account managed by Network Solutions. I also have a standard Mac account (also IMAP) and this problem does not happen. Sometimes, if I open the message and then delete it, it does not reappear in the Inbox, but when I look at the trash, I will have multiple copies of the same trashed message. I have talked to Network Solutions multiple times, but they only "reset" the account and after a few minutes, the problem reappears. This issue does not happen when I open/check this IMAP account with an iPad/iPhone. I am trying to diagnose if the problem is an Outlook problem or if it is a Network Solutions problem. I was about to close the Network Solutions IMAP account and open it at another email provider, but I am not sure who is at fault.

Thank you very much for your help.