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Mimecast · temporary error

452: more than 100 recipients in one message

Mimecast accepts at most 100 recipients per message transaction and asks your server to send the rest in another batch. Most mail servers do this automatically.

Mimecast
Provider
Temporary (4xx)
Class
Sources checked
By , email deliverability consultant
Author

At a glance

Code
452
Provider
Mimecast
Temporary or permanent
TemporaryThe sending server keeps the message and tries again later.
Who has to act
The sender. The fix is on the sending side: your domain, your server or your list.
What the server says
452 Too many recipients.

What it means

By default Mimecast takes up to 100 RCPT TO commands for one message. When a sending server names more, Mimecast answers the extra ones with this temporary reply. The intended behaviour is that your server delivers the message to the first 100 recipients, then opens a new transaction for the next batch, and most servers handle it that way. Delivery fails only where something on the sending side treats the reply as a refusal, which Mimecast says happens with some firewall SMTP inspection features. In that case the recipients past the first hundred do not get the message.

Common causes

  • A single message addressed to more than 100 recipients at domains served by Mimecast.
  • Sending software or a firewall feature that does not respect the reply and fails the extra recipients instead of retrying them.

How to fix it

  1. 01Check whether the recipients past the first hundred actually received the message.
  2. 02If they did not, split the message into batches of at most 100 recipients.
  3. 03Disable firewall SMTP inspection features such as Cisco’s SMTP fixup, which Mimecast names as not respecting this reply.

Sources

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

  1. 452Insufficient system storage.The receiving server is short of storage or has hit a limit, such as the number of recipients in one message, and asks the sender to try again later.StandardTemporary

452 at other providers

  1. 452Too many emails in one session.Your server sent more messages in one SMTP session than Xfinity accepts. Xfinity allows 1,000 emails per session, so the rest have to go in a new session.ComcastTemporary
  2. 452Too many recipients in one message.The message listed more recipients than Xfinity accepts at once. Xfinity allows 100 recipients per message, so a larger list has to be split.ComcastTemporary
  3. 452Too many recipients in one message.Your server named more recipients in one transaction than GMX accepts, currently 20 per message, so the rest were deferred. Split the recipients into several transactions.GMX, WEB.DETemporary
  4. 452Hourly recipient limit reached.Your server sent more recipients to the company’s Cisco gateway this hour than its rate limit allows. The rest are deferred until the limit resets.Cisco Secure EmailTemporary

All 19 Mimecast codesEvery code in the wikiPaste your own bounce

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