452: too 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.
- Comcast
- Provider
- Temporary (4xx)
- Class
- Sources checked
- Author
At a glance
- Code
- 452
- Provider
- Comcast (Xfinity)
- 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 emails sent on this session
What it means
Xfinity caps the number of messages a sending server can deliver over a single SMTP session at 1,000. Once a session reaches that number, Xfinity answers further messages with this 452, a temporary error. The messages themselves are fine: the server only needs to close the session and open a new one for the remainder. Senders who reuse connections heavily can set a per-connection message limit below Xfinity's cap so the error does not appear at all.
Common causes
- Your server delivers many messages over one long-lived connection.
- Connection reuse settings allow more than 1,000 messages per session.
How to fix it
- 01Let the deferred messages retry, since they can be accepted in a new session.
- 02Set a maximum number of messages per connection to Xfinity below 1,000.
- 03Spread volume across several sessions, within Xfinity's limit of 25 simultaneous connections per IP.
Sources
What this page rests on, checked on 20 Oct 2026. The explanation is ours; the reply text is the server's.
Related codes
- 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.
- 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.
452 at other providers
- 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.
- 452More 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.
- 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.
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