BT Email problems: error code 0x800CCC79 (Error 550)

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:

Authentication failure

If you're trying to send email from and to a valid email address and you receive an Error 550 message, check that your email program is set up for SMTP authentication.

To protect our email server from spammers, we only allow our own customers to use it. We do this by insisting that all emails sent through the BT Email service have SMTP authentication to prove where they came from. For more information see How do I set up BT Email on my computer or mobile device? >

Sending from an invalid address

If you're 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're sending from doesn't appear to be valid, our server won't send the email. Please check the following:

Sending to an invalid address

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

If you're 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.

If you're trying to send an email to a different mail server (to an email address that doesn't 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're sending to is spelt correctly
  • There are no service problems with the destination mail server

Further information

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

Using the error message to help fix a fault in BT Yahoo Mail >

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