Sometimes exim is messed up and when you are reviewing the exim_mainlog, you might see the following:
2012-05-11 07:42:16  Failed to get write lock for /var/spool/exim/db/ratelimit.lockfile: timed out
2012-05-11 07:42:16  H= temporarily rejected connection in “connect” ACL: ratelimit database not available
This issue causes because of cache databases corruption and of the presence of db lock files in the path “/var/spool/exim/db/”. Please go ahead and clear all files in that path.
do, rm -rf /var/spool/exim/db/*
then restart exim.
If that didn’t fix, you should empty the “.MYD” files present in the “eximstats” database.
Go to “/var/lib/mysql/eximstats”
# > defers.MYD, > sends.MYD etc
Then please restart exim.