This directory contains important logs such as exim_mainlog, messages, and chkservd.log. While these logs are rotated regularly, archived logs are not deleted. You can safely delete any log that has a .1, .2, .3, or .4 extension, as these are the old archived logs
/var/spool/exim/input/ & /var/spool/exim/msglog/
These files are generated by Exim (the mail server) from bounced emails, or emails waiting to be delivered and are in the message queue. If you notice your /var partition filling up and you have removed your archived logs from section 2.3, then you most likely have a lot of entries in these directories. You should verify the size of this directory to see if it is a problem:
du -h /var/spool/exim/input
du -h /var/spool/exim/msglog
If any of these directories is very large chances are they are the culprit.
You might not notice an immediate difference in disk space used after deleting these logs, but after a few minutes your partition information should be updated which you can view using the command: