4.5.3: too many recipients
The message lists more recipients than the server accepts in one transaction; the remaining recipients have to be sent in a separate transaction.
- Standard
- Provider
- Temporary (4xx)
- Class
- Sources checked
- Author
At a glance
- Code
- 4.5.3
- Provider
- Standard SMTP codes
- 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
4.5.3 Too many recipients
What it means
RFC 3463 expects a sending server that meets this limit to split the message: deliver to the recipients that were accepted, then send the rest in another transaction. RFC 5321 says the right reply for the condition is 452 and that clients should treat it as temporary, which is why 4.5.3 is the usual form. Most mail servers do the split on their own and nobody notices. It turns into a bounce when the software cannot split, or when the receiver enforces a policy limit and answers with a 5xx code instead (5.5.3); then the message must go out to fewer recipients at a time.
Common causes
- One message addressed to more recipients than the receiving server's limit per message.
- A sending tool that puts a whole list into the To, Cc or Bcc fields of one message.
- A site policy that limits recipients per message.
How to fix it
- 01Let the sending server retry: it should send the remaining recipients in a new transaction.
- 02Send bulk mail as one message per recipient, as mailing tools normally do.
- 03If you use a desktop client or a script, split long recipient lists into smaller groups.
- 04If the bounce is permanent (5.5.3), ask the recipient's administrator what the limit is.
Sources
What this page rests on, checked on 20 Oct 2026. The explanation is ours; the reply text is the server's.
Related codes
- 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.
- 4.3.1Receiving system out of storage.The receiving mail server has run out of storage space, so it cannot accept messages for now; the sending server keeps the message and retries later.
4.5.3 at other providers
- 4.5.3Too many recipients from one domain.The message had more than 200 envelope recipients from the same domain, so Microsoft 365 asked the sending server to split it.
- 452 4.5.3Recipient needs its own transaction.The receiving domain's policy settings mean Gmail cannot take this recipient in the same transaction as the others, so it asks you to retry it separately.
- 452 4.5.3Too many recipients.Your message lists more recipients than Gmail accepts at once, so the extra recipients are deferred and need to go in a separate transaction.
All 105 standard codesEvery code in the wikiPaste your own bounce