Email problems: error code 0x800CCC79 (Error 550) - Recipient not authorised/Unknown local user

If you can't send email, your email program may display an error message containing "error code 550" or "error code 0x800CCC79". It may also say "Recipient Not Authorised" or "Unknown Local User". There are three main reasons for receiving these error messages, please see below for the appropriate solution:

Authentication failure

If you are trying to send email from and to a valid email address and you receive an Error 550 message then the first thing to check is that your email program is set up for SMTP authentication.

To protect our email server from abuse by spammers, we only allow our own customers to use it. We do this by insisting that all emails sent through BT Yahoo! have SMTP authentication to prove where they came from. The link below will help you with this problem:

Sending from an invalid address

If you are trying to send email from an invalid email address you'll get an Error 550 message saying: "Server Response: '550 Recipient Not Authorised [recipient rejected due to no authorised destination groups]".

So if the address you are sending from does not appear to be valid, our server will not send the email. Please check the following: 

• The address you are sending from was spelled correctly when you set up your mail account, you may find the link below can help you:
  
   Read an introduction to setting up email
• It is at least 24 hours since the email address was created (this is because it may take our system up to a day to activate a new address).

Sending to an invalid address

If the address you are sending from is valid, then there may be a problem with the address you are sending to.

If you are trying to send an email to an invalid @btinternet.com or @btopenworld.com email address then you'll get an Error 550 message saying: "Server Response: '550 unknown local user".

Alternatively, if you are trying to send an email to a different mail server (to an email address that does not contain @btinternet or @btopenworld) then you may receive a "Delivery Status Notification (Failure)" email from the destination mail server.

Please check the following: 

• The address you are sending to is spelled correctly.
• There are no service problems with the destination mail server.

Further information

If you're having problems with your emails or your're receiving error messages, please use the link below for further information about error messages and how to resolve them: