The recipient's email address doesn't exist or the mailbox is unavailable. This is a permanent error.
SMTP error 550 is one of the most common email errors. It indicates that the email could not be delivered because:
The email address has a typo or the user account was deleted.
Your IP or domain is blacklisted by the recipient's server.
The recipient's mail server has policies that block your message.
Your email authentication records are missing or misconfigured.
Double-check the recipient's email address for typos. Try contacting them through another channel to confirm their current email.
Use our Blacklist Checker to see if your domain or IP is listed on any blacklists. Request removal if listed.
Ensure your domain has proper email authentication records. This helps receiving servers trust your emails.
If you're certain the address is correct, the recipient's IT team may need to whitelist your domain.
550 5.1.1 <[email protected]>: Recipient address rejected: User unknown in virtual mailbox table
550 5.7.1 Service unavailable; Client host [x.x.x.x] blocked using Spamhaus
550 Requested action not taken: mailbox unavailable