Author: j2 Date: To: Peter Bowyer, exim-users Subject: Re: [Exim] Ignore freezes due to unknown user in 4.40?
> accept domains = +relay_to_domains
> verify = recipient/callout=10s
>
> This will do a recipient callout to the backend server before accepting
> the message. Results will be cached so you get no extra overhead for
> commonly-occuring valid users.