13.10. Customizing Prohibition Messages

It is possible to add a site-specific message to the error response that is sent when an incoming SMTP command fails for policy reasons; for example, if the sending host is in a host reject list or if relaying is prohibited. This is done by setting the option prohibition_message, which causes one or more additional response lines with the same error code and a multiline marker to be output before the standard response line. For example, setting:

prohibition_message = contact postmaster@my.site for details