for the past 10 days i keep on receiving an admin error report like this

postdrop (total: 1)
1 uid=0: File too large

Fatal Errors
sendmail (total: 1)
1 root(0): message file too big

please help how can i fix this problem. though email is working fine, im afraid it could cause real fatal error.

what particular file here is "too big" and where can i find it? should i be bother also? help please. thanks.

*there is no send mail running
[root@mail ~]# service sendmail status
sendmail: unrecognized service

im using:
zimbra open source v8
centos 6.3