[Exim] query about verifying aliases

I was slightly surprised to discover the following although The Fine Manual
does indeed spell out why it happens this way.

We have (historically always had) aliases for each of our users a bit like
this :-

full.name: username
username: username@mailhost

If they move on, we might change the second line to forward their SPAM ;-) etc.
If they leave without trace, or start getting their own SPAM directly, we
might change the second line to the handy ":fail: thank goodness this chap
left" thing.

We also enable "verify_recipient" - in the hope of repelling misaddressed SPAM
before it gets into our queue, giving us the headache of replying ...

Now, I only just noticed that this has the effect of leaving the first alias
as valid for the verification in our system_aliases director, so that SPAM
sent to the second (:fail:) address does get refused but stuff sent to the
first address (that we didn't change) gets accepted and generates a
mailer-daemon error reply.

Also, I notice that "exim -bv full.name" verifies but "exim -v -bv full.name"
does not verify - as per the words in TFM - just like "exim -bt full.name"
fails.


So what I want to ask is, does anyone have any suggestions in this situation?
Having advertised/supported both email addresses in the past I'd like to try
to do something helpful with mail to either address.

I guess I could just remove the first alias (turn it into a comment perhaps)
or replace it with another :fail: - or is there some option to the director
that would make verifying more like an attempted delivery?

Thanks ,

Steve Platt