[exim] Delete frozen messages

Hi!

I want to configure Exim to delete frozen messages after two hours. I've
this parameters in exim.conf:

ignore_bounce_errors_after = 2h
timeout_frozen_after = 2h

but Exim doesn't delete frozen messages. The frozen messages in the queue
are like these:

[xxxx@yyyyyyyy exim]$ /usr/sbin/exim -bp | grep frozen | more
16h 2.1K 1Hpu6h-0008Vu-0B <> *** frozen ***
9h 2.1K 1Hq10K-0006Sg-3a <> *** frozen ***
9h 1.8K 1Hq1UK-0003uQ-U7 <> *** frozen ***
9h 2.6K 1Hq1Uu-0004VV-N6 <> *** frozen ***
9h 3.1K 1Hq1Ve-0004p9-3x <> *** frozen ***
9h 2.5K 1Hq1Wz-0005Rf-Es <> *** frozen ***
9h 2.2K 1Hq1Xj-0005fc-Ru <> *** frozen ***
9h 2.8K 1Hq1YI-0005uz-K1 <> *** frozen ***
8h 1.9K 1Hq1Yu-0006BQ-L4 <> *** frozen ***
8h 3.1K 1Hq1ZS-0006NY-Dq <> *** frozen ***
...

How can I get frozen messages deleted at two hours?