[Exim] timeout_frozen_after and

Our Exim config contains:

timeout_frozen_after = 7d

Therefore I was surprised to see:

$ mailq | head -n 2
73d  1.3K 191TFb-0002il-00 <> *** frozen ***
          6a@???

I tried:

$ exim -v -M 191TFb-0002il-00

delivering message 191TFb-0002il-00
LOG: 0 MAIN
Unfrozen by errmsg timer
LOG: 0 MAIN
lowest numbered MX record points to local host: 6abc.com
LOG: 0 MAIN
== 6a@??? R=lookuphost defer (-1): lowest numbered MX record
points to local host
LOG: 0 MAIN
Frozen

It seems that all messages in this state are frozen with either the
above message, or remote host is local host.

(The lowest MX for that domain is indeed 127.0.0.1, and other messages
were addressed to our machine by hostname, rather than by a domain that
we host)

Is there a good reason why these messages are exempt from the
"timeout_frozen_after" handling?

Paul