Server Error: 551, Error Number: 0x800CCC79

My wife is having an intermittent problem sending email.

Windows Vista, using Windows Mail. Bellsouth.net is the ISP. POP3. She uses her @bellsouth.net email account.

Several times in the last week she gets an error message when she attempts to send mail. She has the correct addresses, everything in the email account properties looks okay to me (I have checked other threads here). The problem may last for an hour or two, or the outbound mail may go ten minutes later when closing Windows Mail. Or it may just go the 25th time you hit "Send/Receive Mail," which is what just happened. I wanted to double check that I had the entire error message so I hit send/receive again and the message went out!

This just started happening about a week and a half ago, and it happens more than once every two days.

Error message from Windows Mail:

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 'xxxxxx@gmail.com'. Subject 'Dinner', Account: 'mail.bellsouth.net', Server: 'mail.bellsouth.net', Protocol: SMTP, Server Response: '551 not our customer', Port: 25, Secure(SSL): No, Server Error: 551, Error Number: 0x800CCC79

Intermittent problems are the best!

Thanks for help or advice -- her mail is making its way out eventually but every time there is a hang up I get an exasperated call to come fix.

That seems to say that the email address you're sending to is invalid. You should verify the address. It appears that you have not setup users / ips that can use their SMTP server to send to remote recipients (authenticated logins or allows specific IP addresses to use the server), for example - the SMTP server does not let anyone, send mail through it anywhere, as it permit spammers to make use of to relay mail. I hope this will help you to understand your difficulty thank you.