Let’s take a short look at the list of possible reasons due to why a user may encounter error code 550 in the SBCGlobal email account;
The recipient’s email address is wrong or does not exist.
The recipient’s email server fails to identify your SBCGlobal email address.
Your email account domain name is invalid or blocked.
If you are using your email client through a different IP address, then it can lead to SBCGlobal email error 550.
Regards,
Rachel Gomez