can't send email to certain addresses

Couldn't send to my husband's work address suddenly. I could send to his work address from our other laptop. I asked him to look into it. As part of that, he got on my laptop and forwarded an email to our home email that he then tried to send to his work address in hopes he could troubleshoot at work. Now the problem has "spread" to his laptop. Now we both can't send anything to his work address from either of our computers. Here's the error message, which pops up with our without outgoing authentication checked:

The message could not be sent. The authentication setting might not be correct for your outgoing e-mail [SMTP] server. For help solving this problem, go to Help, search for "Troubleshoot Windows Mail", and read the "I'm having problems sending e-mail" section. If you need help determining the proper server settings, please contact your e-mail service provider.
The rejected e-mail address was '****@centcom.mil'. Subject 'Fw: send this to my work', Account: 'POP-SERVER.tampabay.rr.com', Server: 'smtp-server.tampabay.rr.com', Protocol: SMTP, Server Response: '450 4.1.8 - Domain of recipient does not resolve [R0309001]', Port: 25, Secure(SSL): No, Server Error: 450, Error Number: 0x800CCC79

Any help would be greatly appreciated!

Other than the address anything unique about those emails; pictures, links, etc.

Try with your antivirus off.

Try adjusting the security settings under the tools tab ( I am assuming windows mail or windows live mail)