I run an Exim mail server with multiple virtual domains (a setup similar to this). The server is the smarthost for some other servers.
Suppose I have a virtual domain example.com which has a redirect: foo@example.com =>bar@example.org.
When a server wants to use this Exim server to send mail to foo@example.com, I expect that the mail server sends the mail bar@example.org.
All fine so far, but what if the example.com MX record did not point to this Exim server? Then delivering the mail to bar@example.org would be incorrect.
Is there a way make Exim check MX record validity when using those virtual domain rules? If not, what should I do? The virtual domain list is quite long. Writing a cron script to invalidate (and re-validate) any invalid domains would feel wrong, or at least a bit hacky.