My MX servers have no mailboxes. They either relay email to an external
domain address the user asked to have set up, or they relay to one of three
servers within our domain. We use :
virtual_alias_maps = hash:/etc/postfix/relocated
virtual_alias_domains = $virtual_alias_maps, mydomain.ca
The virtual file contains every address we handle in one of these ways.
I can't see using reject_unverified_recipient for the volume of email we
and it is pointless to do when we have a valid list of all addresses
the MX should handle.
In main.cf I see:
# The relay_domains parameter restricts what destinations this system will
# relay mail to.
The list of domains we forward to, based on the virtual mapping file,
will vary over time, so there is no easy way to satisfy the
requirements of relay_recipient_map.
Based on what I'm seeing in our logs, and from swaks talking to our MX
I have to conclude that relay_recipient_map is not the only way to disable
backscatter. The documentation should include mention of virtual_alias_maps
as being another alternative which allows reject prior to queueing.
With relay_domain and mydestination set to null, we are getting useful
rejects. From swaks I test email to non-existant address:
=== Trying nexa.mydomain.ca:9077...
=== Connected to nexa.mydomain.ca.
<- 220 nexa.mydomain.ca ESMTP Postfix
-> EHLO somewhere.ca
<- 250-SIZE 10000000
<- 250 DSN
-> MAIL FROM:< ... at somewhere dot ca>
<- 250 2.1.0 Ok
-> RCPT TO:<donald. ... at mydomain dot ca>
<** 550 5.1.1 <donald. ... at mydomain dot ca>: Recipient address rejected: User
unknown in virtual alias table
<- 221 2.0.0 Bye
=== Connection closed with remote host.
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