What the message looks like
554 5.5.2 Helo command rejected: need fully-qualified hostname504 5.5.2 Helo command rejected: need fully-qualified hostname
What it means
When one mail server connects to another, it introduces itself with a HELO or EHLO command that includes its hostname. The receiving server rejected that name because it isn't a fully-qualified hostname, such as mail.example.com. The standard name for this status is "syntax error".
Common causes
- The sending server introduces itself as
localhost, a bare name likeserver1, or an IP address. - A website, printer, scanner or app sending email directly instead of through a proper mail provider.
- A newly set up mail server whose hostname hasn't been configured.
If you're the recipient
There's nothing to change on your side. If you can, let the sender know their emails are being rejected and pass on the error message.
If you're the sender
Set your mail server's hostname to a fully-qualified name that exists in DNS and matches the reverse DNS (PTR) record of its IP address. In Postfix this is the myhostname setting. If the email comes from a website or app, send through an established email provider instead of directly from the server.
If you use addy.io
addy.io rejects these emails with 554 5.5.2 Helo command rejected: need fully-qualified hostname before they reach your alias. You can't fix this from your account. The sender's server administrator has to fix it. See inbound rejections.