Did any members get the message?

Usually not when the whole expansion failed. If only one member failed, you would see a separate bounce for that address instead.

Is 5.2.4 a permission error?

By definition it is an expansion problem, but some servers use it when outside senders may not post to a group. The bounce text usually says which.

5.2.4 bounce: mailing list expansion problem

5.2.4Mailing list expansion problemPermanent: retrying will not help

Typical wording

550 5.2.4 <team@example.com>: Mailing list expansion problem

What it means

RFC 3463 defines X.2.4 as "Mailing list expansion problem". The address you wrote to is a list, alias, or distribution group, and the server could not turn it into the list of member addresses. The address itself was valid; the failure happened when the server tried to fan the message out.

Exchange has used 5.2.4 for distribution group problems, for example a dynamic group whose query failed or a group the sender may not post to. Mailing list managers and Sendmail alias files can produce it when the alias file is broken or a member address is invalid. The difference from 5.1.1 is that the list was found, and the difference from 5.7.1 is that the problem is expansion, not permission (although some systems blur the two).

A 4.2.4 appears when the directory or list database could not be reached, and the sender retries. A 5.2.4 means the list is broken or refuses expansion for this message.

Likely causes

A dynamic distribution group whose filter references a missing attribute or directory container.
A group restricted to internal senders or a list of approved senders, reported with 5.2.4 instead of 5.7.1.
A nested group loop, or a group that contains a contact pointing back at the group itself.
An alias or list file with a syntax error or a member address that cannot be parsed.

How to fix it

As the sender, tell the list owner, including the full bounce. You cannot fix expansion from outside.
As the group owner, check delivery restrictions, approved sender lists, and whether external senders are allowed.
Validate the group membership or dynamic filter and remove members that point back at the group or at deleted objects.
For alias files, run the MTA’s alias rebuild command (for example `newaliases`) and fix any errors it prints.
Send a test message from both an internal and an external account after the change.

Checks that apply

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

MX Lookup Shows which provider hosts the group, which tells the owner which admin console to use.
MailFlow Monitor Lets the list owner send monitored test mail to the group and confirm expansion now works.

FAQ

Did any members get the message?: Usually not when the whole expansion failed. If only one member failed, you would see a separate bounce for that address instead.
Is 5.2.4 a permission error?: By definition it is an expansion problem, but some servers use it when outside senders may not post to a group. The bounce text usually says which.

All 191 bounce codes