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✉️ Email Delivery

Documentation, reference material and tutorials for CRM-NG SMTP Email: setup guides for every mail service, troubleshooting, and one article per error message.

Error: 452 4.5.3 Domain policy size per transaction exceeded

Updated

By Duane GarnerChief Executive Officer (CEO)
Summarize: Claude ChatGPT View Markdown
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One email was addressed to more recipients than the server allows per message. Split it into smaller sends or trim CC and BCC lists.

Shown by SMTP-based sending (Other SMTP, Zoho Mail, the backup SMTP transport)

The test result or the error log shows a reply such as 452 4.5.3 Domain policy size per transaction exceeded, or another reply starting with 452.

This article is for site owners sending through an SMTP server whose email is refused because it has too many recipients.

What this error means

Reply 452 means the server cannot accept more right now. With the detail 4.5.3, the limit is the number of recipients in one message: the server's policy sets a maximum per send, and your message went over it. The server usually accepts the first recipients up to the limit and refuses the rest, so some people may get the email while others do not.

The 4 at the start makes it temporary in SMTP terms, but sending the same message again will hit the same limit. The message has to be split.

Common causes

  • A plugin sends one message to a long list of addresses in To, CC or BCC, such as all admins, all members or all event attendees.
  • A form notification lists many recipients.
  • A shared hosting or business mail server with a low per-message recipient cap.
  • Less often, 452 4.3.1 (a different detail code) means the server is short of storage; that one clears on its own.

How to fix

  1. Find the message

    Open CRM-NG SMTP → Settings → Email Log, open the failed entry and check how many recipients it had and which plugin sent it.

  2. Ask about the limit

    Ask your mail provider how many recipients one message may have. Business mail servers often allow somewhere between a few dozen and a few hundred.

  3. Split the sending

    Change the sending plugin so it sends one message per recipient or small batches. Many newsletter, membership and form plugins have a setting for this.

  4. Keep test sends small

    Go to CRM-NG SMTP → Tools → Email Test, fill in Send To with one address and press Send Email to confirm the connection itself works.

  5. Pace large sends

    Go to CRM-NG SMTP → Settings → Misc and set Email Rate Limiting so many single messages do not trip a separate hourly limit.

Verify it worked

The test email arrives, and when the sending plugin runs again, the Email Log shows separate successful entries instead of one failed entry with many recipients.

Notes

  • Keeping each email to under about ten recipients avoids most per-message limits and also looks less like bulk mail to spam filters.
  • For true bulk mail such as newsletters, use a service made for it. Most API mailers handle large sends far better than a mailbox's SMTP server.
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