Skip to content
MailVitals Email deliverability
Sign inEarly access
Standard SMTP codes · permanent error

5.2.4: mailing list could not be expanded

The address is a mailing list, and the server could not turn it into the list of member addresses, so the message did not go out to the list.

Standard
Provider
Permanent (5xx)
Class
Sources checked
By , email deliverability consultant
Author

At a glance

Code
5.2.4
Temporary or permanent
PermanentRefused for good: the message comes back to the sender, and resending it gets the same answer.
Who has to act
The recipient's side. Their mail admin has to change something; you can tell them.
What the server says
5.2.4 Mailing list expansion problem

What it means

Some addresses are lists that the receiving server expands into many recipients. X.2.4 says the expansion failed: the member data could not be read, the list is misconfigured, or it refers back to itself. RFC 3463 says it may be a permanent or a persistent temporary failure. 5.2.4 means the message was returned; 4.2.4 means the server will accept a retry once the list works again. The sender cannot repair a broken list, but can tell the list's owner or the postmaster address at the recipient's domain.

Common causes

  • A list whose member database or file could not be read.
  • A misconfigured list, for example one that includes itself.
  • A list on a server that is being moved or rebuilt.

How to fix it

  1. 01For 4.2.4, wait for the retries.
  2. 02Tell the list owner, or the domain's postmaster address, about the bounce.
  3. 03If members must be reached urgently, write to them directly.
  4. 04List admins: check the list's membership source and remove any loop.

Sources

What this page rests on, checked on 20 Oct 2026. The explanation is ours; the reply text is the server's.

  1. 5.7.2Not allowed to send to this list.The sender is not authorised to post to the mailing list it wrote to, so the list refused the message.StandardPermanent
  2. 5.4.6Mail routing loop.The message was passed back and forth between servers, or forwarded around a circle, until a server noticed the loop and stopped it.StandardPermanent

All 105 standard codesEvery code in the wikiPaste your own bounce

Beat · paid monitoring

A heartbeat for your email.

Beat runs every check on this site on a schedule: 41 checks, 33 blacklists and real inbox placement. The moment something breaks, it tells you what broke, why it matters, and the exact fix.

Get early access to BeatSee what Beat watches
example.comWatching
  • SPFpass
  • DKIMpass
  • DMARCp=none
  • Blacklists0 of 33

Illustrative. Your domain, every few hours.

Also from us:Pulse: your own sending infrastructureConsulting: $65/hr, no retainer