Did my message reach anyone on the list?

No. The server refused to expand the list, so no member received it.

The list owner or the recipient’s mail admin. A sender cannot change a list’s posting policy.

5.7.2 bounce: mailing list expansion prohibited

5.7.2Mailing list expansion prohibitedPermanent: retrying will not help

Typical wording

550 5.7.2 Mailing list expansion prohibited for sender user@example.com

What it means

X.7.2 is “mailing list expansion prohibited” in RFC 3463. The address you wrote to is a list or group, and its policy does not allow you to post. The server knows the address exists, so this is not an unknown-recipient error; it simply will not expand the list for you.

You see it with moderated or members-only lists, distribution groups restricted to internal senders, and groups with an allow list of posters. Some list servers return 5.7.2 at SMTP time; others accept the message and later send a separate rejection notice.

The temporary form 4.7.2 is rare. A list that refuses your post today will usually refuse tomorrow, unless the owner changes its settings.

Likely causes

The group only accepts mail from people inside the organisation, and you are an external sender.
The list is members-only and your address is not subscribed, or you posted from a different address than the one subscribed.
The group has a list of approved senders that does not include you.
Your From address changed (for example through a forwarding service) so the list no longer recognises you.

How to fix it

Check that you posted from the exact address that is subscribed or approved.
If you are external, ask a member or the list owner to allow your address, or ask for an individual address instead.
If you administer the group, review its delivery settings; in many groupware products the option is called something like “allow external senders”.
After the change, send a short test to the list and confirm it is delivered rather than rejected.

Checks that apply

Your domain or sending IP (fills in the checks below)

MX Lookup Confirms the list domain and its mail servers, which helps when the list is hosted on a separate list-management service.
Email Header Analyzer Shows the From and envelope addresses your message really carried, useful when the list did not recognise you.

FAQ

Did my message reach anyone on the list?: No. The server refused to expand the list, so no member received it.
Who can fix a 5.7.2?: The list owner or the recipient’s mail admin. A sender cannot change a list’s posting policy.

All 191 bounce codes