[CentOS] logrotate failed ... (CentOS 6.9)

I get regularily such a mail

<mail>
Anacron job 'cron.daily' on ....

/etc/cron.daily/logrotate:

error: error running non-shared postrotate script for 
/var/log/clamd.clamsmtp/clamsmtpd.log of 
'/var/log/clamd.clamsmtp/clamsmtpd.log '
</mail>

content of /etc/logrotate.d/clamsmtp

/var/log/clamd.clamsmtp/clamsmtpd.log {
     monthly
     notifempty
     missingok

     postrotate
         pkill -SIGHUP -f clamd.clamsmtp >/dev/null 2>&1 || :
     endscript
}

when looking at  ls:

<ls -al /var/log/clamd.clamsmtp/>
total 572
drwxr-xr-x. 2 clamsmtp mail   4096 May  1 03:15 .
drwxr-xr-x. 6 root     root   4096 May  1 03:15 ..
-rw-r-----. 1 clamsmtp mail    953 May  1 08:43 clamsmtpd.log
-rw-r-----. 1 clamsmtp mail 109806 Jan  1 10:28 clamsmtpd.log-20170101
-rw-r-----. 1 clamsmtp mail 114825 Feb  1 03:42 clamsmtpd.log-20170201
-rw-r-----. 1 clamsmtp mail 101356 Mar  1 03:50 clamsmtpd.log-20170301
-rw-r-----. 1 clamsmtp mail 112365 Apr  1 19:51 clamsmtpd.log-20170401
-rw-r-----. 1 clamsmtp mail 104204 May  1 03:15 clamsmtpd.log-20170501
</ls>

this shows normal

where does this error mail come from?

Thanks
Walter