InterScan Messaging Security Virtual Appliance (IMSVA) uses Postfix to receive and send emails, and the parameter "smtpd_recipient_limit" in the main.cf file is used by Postfix. If the number of recipients in an email exceeds the value of "smtpd_recipient_limit", IMSVA will respond "452 too many recipients". If you continue to send using the "RCPT TO" command, the recipients that exceed the value will be discarded by IMSVA. Thus, some email servers may separate the email when receiving the "452 error code", while others may separate the email with many recipients by default.
It is recommended to keep the default value of "smtpd_recipient_limit". Also, we suggest you to enable the condition Number of recipients is in the policy, as it can reject the email when recipients in "RCPT TO" command exceed the value you set.
If the email has been separated by the email sender, create a regular expression to block the email with more than 40 recipients.
- Go to Policy Objects > Keyword Expressions to create an expression.
- List Name: email_addr_in_header
- Match: All specified
The following sample matches more than 40 email addresses.
- Create a rule in the policy list page with the following configuration:
- Recipients and senders is Anyone to anyone.
- Action is set to Quarantine.
- Edit the Scanning Conditions, and select the Header keyword expressions.
Below is sample configuration:
- Save the policy and verify it in your environment.
