[pfx] Re: Question about the parameter: permit_mx_backup_networks

On Sat, 25 Jul 2026 07:06:00 -0400 (EDT)
Wietse Venema via Postfix-users <[email protected]> wrote:

> Klaus Tachtler via Postfix-users:
[snip]
> > 
> > Does the `permit_mx_backup_networks` parameter still have any 
> > significance at all?  
> 
> permit_mx_backup was maybe useful 30+ years ago.
> 
> Nowadays, a backup MX host needs to know who are the valid
> recipients, otherwise the backup MX accepts spam for a non-existent
> recipient, tries to deliver it to the backed-up domain, and then
> tries to return it to a sender who did not send that spam.

Aka: "Accept and bounce." A good way to end up on one-or-more
blacklists.

Regards,
Jim
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