Problem with the number of recipients in email

Support and Discussion General Discussion
1

Hi, this is my first post about one of the problems I’m having.
For a while now, I haven’t been able to send emails to more than 10 recipients at a time from Outlook or SnappyMail. If I add 11 recipients, I get the error “Message cannot be sent” “451 4.7.1 Ratelimit ‘customrl’ exceeded.”
I don’t know if something has been misconfigured in Cyberpanel or what happened, but all the accounts on all the domains I manage with Cyberpanel are showing the same error.
Can anyone help me?

Thank you very much.

2

1. Understand the “customrl” Ratelimit Error

  • The error 451 4.7.1 Ratelimit ‘customrl’ exceeded typically indicates that your mail server has a custom rate-limiting or recipient-limit policy enabled. In CyberPanel (which generally uses Postfix + some policy daemon under the hood), this policy blocks or temp-fails email once a certain threshold is reached.
  • The limit can be imposed on total recipients per message, number of messages per time period, or both.

2. Check CyberPanel’s Email Limit Settings

  1. Log in to CyberPanel and navigate to Email → Limits (or sometimes Email → Email Policy depending on CyberPanel version).
  2. Look for any configured policies, such as:
  • Max Recipients per message
  • Max hourly emails per domain or per account
  • Global rate-limits

If you find a “Recipients per message” limit set at 10, you can raise it to a higher number (e.g., 20, 50, etc.) or disable the policy temporarily if appropriate.

Note: If you have multiple domains and packages, make sure the package/domain assignment isn’t enforcing a default limit on recipients. Sometimes you must edit the package or plan assigned to that domain/account to change email sending limits.

3. Look in Postfix (or Policyd) Config Files (Advanced)

If you cannot locate the relevant setting in CyberPanel’s GUI, or if changes in the GUI do not resolve the limit, it may be stored in a Postfix policy service or a custom config file:

  1. Check Postfix config:
  • Files to examine: /etc/postfix/main.cf, /etc/postfix/master.cf
  • Look for lines like smtpd_recipient_limit, smtpd_limit_extensions, or references to “policy”/“policyd.”
  1. Check Policyd / Rate-limit Daemon config:
  • Some setups use postfwd or policyd for advanced rate-limits.
  • See if there is a config file in /etc/postfix-policyd.conf or similar that references customrl.
  • If you see something like MAX_RCPTS=10, raise it as needed.
  1. Restart Postfix:
    After any changes, reload or restart the Postfix service to apply them:
sudo systemctl restart postfix

4. Confirm Logs and Check for Conflicts

  • Mail logs: Watch /var/log/maillog (or /var/log/mail.log on some systems) when sending messages. Search for “customrl” or “ratelimit” to confirm which policy is enforcing the limit.
  • Overlap with ClamAV/Amavis/SpamAssassin: If you run other anti-spam layers, confirm none of them are also imposing a separate outbound limit.

5. Test with Different Accounts or Domains

  • If all domains on the server share the same symptom, it’s likely a global or server-wide policy in CyberPanel or Postfix.
  • If it only happens under certain mailboxes or domains, the setting might be domain-specific.

6. Last Resort: Temporarily Disable or Increase the Ratelimit

If you absolutely need to send emails to more than 10 recipients, try:

  1. Increase the threshold: For example, set max recipients to 50 or 100.
  2. Disable the rate-limit: Not recommended long-term (it can risk spam/blacklisting if compromised), but you can test this to see if the error goes away.

Be sure to put a reasonable cap or security measure in place after testing, since eliminating rate limits entirely can expose your server to spam issues or IP blacklisting.