554 5.7.1 Client host rejected or relay access denied

What the message looks like

• 554 5.7.1 Client host rejected: cannot find your reverse hostname
• 554 5.7.1 Helo command rejected: Host not found
• 554 5.7.1 Service unavailable; Client host blocked using zen.spamhaus.org
• 554 5.7.1 Relay access denied

What it means

The receiving server refused the connection or the email because of a rule about the sending server. The standard name for this status is "delivery not authorized, message refused". The 554 reply code is often used when the server rejects the sender as a whole, rather than one email.

Common versions

• Client host rejected: cannot find your reverse hostname - the sending server's IP address has no reverse DNS (PTR) record, or the PTR record doesn't match.
• Helo command rejected: Host not found - the hostname the sending server introduced itself with doesn't exist in DNS.
• Client host blocked using ... - the sending server's IP address is on the DNS blocklist named in the message, such as Spamhaus.
• Relay access denied - the server was asked to deliver mail for a domain it doesn't handle. This usually means the recipient's domain is pointing at the wrong mail server, or the sender is using the wrong server to send.

If you're the recipient

There's usually nothing to change on your side, apart from relay errors on your own domain. If senders get Relay access denied when emailing your domain, check its MX records point to your current email provider.

If you're the sender

Ask whoever runs your mail server to set a reverse DNS record for its IP address that matches a hostname which resolves back to the same IP, and to use that hostname in HELO. If you're on a blocklist, find out why on the blocklist's website and request removal once it's fixed. Sending through an established email provider avoids most of these problems.

If you use addy.io

addy.io sends these rejections when the sending server fails basic checks, before the email reaches your alias. You can't fix them from your account. The sender's email provider or server administrator has to fix them. See inbound rejections.

If senders get 554 5.7.1 Relay access denied when emailing your own domain, check its MX records match the ones shown on your Domains page in addy.io.