Sending’ reported error (0x800CCC7D)

I am frequently getting this error message:
Sending’ reported error (0x800CCC7D) : ‘The connection with the server was interrupted…, please contact your server administrator or Internet service provider (ISP).’

The message is stuck in the Outbox. This happens with only one of several accounts I have in my computer — differnet mail servers/different configs.

The matter is, when you try to TEST the account settings from Outlook, the email gets SENT!!!

I’ve tried everything I’ve come across but they do not help. Please help!