This article discusses why '550 Sender verify failed' messages may occur when you try to send e-mail, and how to resolve the issue.
When you try to send an e-mail message, you receive the following SMTP error message:
550 Sender verify failed
This error message occurs when the sender e-mail account does not exist in cPanel, or when the domain's MX entry records are misconfigured in cPanel.
For example, suppose you add a parked domain, an addon domain, or even an entire cPanel account (if you are a reseller). If the domain's MX records (as set at the domain registrar) point to an external e-mail provider, you must also configure the MX entries in cPanel to use the external e-mail provider. Additionally, in cPanel you must create the e-mail accounts that you want to use to send messages.
To resolve this issue, follow these steps:
Make sure the domain is configured to use the remote e-mail provider.