Investigate why mails are frozen
The exim documentation Show archive.org snapshot says:
Freezing occurs when a bounce message encounters a permanent failure because the sender address of the original message that caused the bounce is invalid, so the bounce cannot be delivered. This is probably the most common case, but there are also other conditions that cause freezing, and frozen messages are not always bounce messages.
By default, frozen bounce messages will be deleted after 2 days and other messages after 7 days. This post on stackoverflow Show archive.org snapshot shows a good way to search for reasons why messages are frozen.
examine the frozen mail/s
# list all frozen mails
exiqgrep -z -i
# print the whole message
exim -Mvc $messageid
# print all frozen messages
exiqgrep -z -i | xargs -n 1 exim -Mvc | less
Delete frozen mails in the queue
Maybe you should check which messages are frozen and search for reasons before you delete them. You should ensure that the mails you will delete are just garbage and nothing important.
exiqgrep -z -i | xargs exim -Mrm
