Mailborder servers automatically perform recipient verification by querying the internal server.
Recipient verification enables the Postfix MTA to accept or reject email based on the existence of the destination email account. The internal server is queried to see if an email is valid. If the internal server responds that it is valid, the email will be accepted by Mailborder. The results are cached.
In order for this to work correctly, the internal email server must be configured to reject email for users that do not exist. Otherwise, Mailborder is going to accept all email for your domains because the internal server is accepting all email for each respective domain.
Resetting the Verification Cache
To reset the Postfix recipient verification cache, first stop the Postfix service:
systemctl stop postfix
then delete this file:
and then restart the Postfix service:
systemctl start postfix
This must be done on each Mailborder server.