550 “Administrative Prohibition” or "Relay Access Denied"
The 550 “administrative prohibition” or “relay access denied” bounce error is generated when a recipient mail server detects that our service hasn’t been given consent to send email on behalf of the sender domain, which is deemed suspicious and subsequently blocked.
This error can be resolved by verifying the Sender Domain. If the error message persists with a verified sender domain, have the recipient whitelist our sending IP addresses with their incoming mail server.
Note: High volume accounts may have their recipients whitelist their dedicated IP address(es) instead of our entire range of sending IPs. Check the “Settings > Dedicated IPs” section of the account’s dashboard to identify the correct address(es) to whitelist.