Can't reply to emails. Sending new ones seems okay.

Last week all of a sudden, my outbox messages would not send.

The error I receive is:

Your server has unexpectedly terminated the connection. Possible causes for this include server problems, network problems, or a long period of inactivity.

Subject 'Re: Samples of new web site design'
Server: 'smtpout.secureserver.net'
Windows Live Mail Error ID: 0x800CCC0F
Protocol: SMTP
Port: 80
Secure(SSL): No
Socket Error: 10053

Today I tested sending several brand new emails and that works fine.

Can someone help figure out what caused this issue to arise and help me fix?

Thanks!