Unknown error message

dovecot 2.3.6 (7eab80676) FreeBSD 12.0-RELEASE-p5 amd64

I have recently been finding error messages similar to the following in my Dovecot log file:

May 26 06:58:32 imap(gerard@seibercom.net)<87791>: Error: stat(/var/mail/vmail/seibercom.net/gerard/.dovecot.sieve/tmp) failed: Not a directory

The message is correct as there is no such directory. The question is why has it suddenly started appearing? I checked my maillog file, and there are no messages being transmitted to Dovecot when that error message is created. Neither is there any mail with that ID number either.

Could this be someone attempting to hack into my system?

Thanks!

-- Jerry