Well clearly the logger folder is the one hogging all the space.
you can clean the logger by deleteing and recreating it..
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Open Source Edition Backup Procedure - Zimbra :: Wiki
Backup your full zimbra install before running the following steps.
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log into zimbra server and run all the following in a sequence
su - zimbra
logmysql.server stop
logout
rm -rf /opt/zimbra/logger/db/data/*
chown zimbra:zimbra /opt/zimbra/db/data
chmod 775 /opt/zimbra/db/data
cd /opt/zimbra/libexec
./zmloggerinit
./zmfixperms --verbose --extended
su - zimbra
zmlogswatchctl start
After this your HDD usage of Zimbra install willl be 6 GB instead of 32 GB
Raj