Issue Internal greylisting: Plesk defers mails sent from console / by scripts as well as internally forwarded mails

[B_P]

Dear all,

By chance I noticed today that my server (Ubuntu 16.04.6, Obsidian 18.0.27, Postfix/Dovecot) seems to apply greylisting not only for incoming messages from other servers but also for mails that are processed locally:
a) for messages that I send from a console, e.g. with "mail [email protected]"
b) for message sent by scripts
c) for messages that the server receives from anywhere and that are then forwarded to another (internal or external) address.

Here's a copy from the corresponding /var/log/maillog when trying case a):
May 23 23:02:29 srv1 plesk sendmail[26145]: handlers_stderr: PASS
May 23 23:02:29 srv1 plesk sendmail[26145]: PASS during call 'limit-out' handler
May 23 23:02:29 srv1 check-quota[26148]: Starting the check-quota filter...
May 23 23:02:29 srv1 plesk sendmail[26145]: handlers_stderr: SKIP
May 23 23:02:29 srv1 plesk sendmail[26145]: SKIP during call 'check-quota' handler
May 23 23:02:29 srv1 dk_sign[26150]: Starting the dk_sign filter...
May 23 23:02:29 srv1 dk_sign[26150]: DKIM error: DKIM Feed: Syntax error
May 23 23:02:29 srv1 plesk sendmail[26145]: Error during 'dd51-domainkeys' handler
May 23 23:02:29 srv1 postfix/pickup[23774]: ED51CA02BF: uid=0 from=<root>
May 23 23:02:29 srv1 postfix/cleanup[26112]: ED51CA02BF: message-id=<[email protected]>
May 23 23:02:29 srv1 greylisting filter[26154]: Starting greylisting filter...
May 23 23:02:30 srv1 psa-pc-remote[4135]: handlers_stderr: DEFER
May 23 23:02:30 srv1 psa-pc-remote[4135]: DEFER during call 'grey' handler
May 23 23:02:30 srv1 psa-pc-remote[4135]: Message aborted.
May 23 23:02:30 srv1 postfix/cleanup[26112]: ED51CA02BF: milter-reject: DATA from localhost[127.0.0.1]: 4.7.1 Service unavailable - try again later; from=<[email protected]> to=<[email protected]>
May 23 23:02:36 srv1 postfix/pickup[23774]: 11635A02BF: uid=0 from=<root>
May 23 23:02:36 srv1 postfix/cleanup[26112]: 11635A02BF: message-id=<[email protected]>
May 23 23:02:36 srv1 greylisting filter[26156]: Starting greylisting filter...
May 23 23:02:36 srv1 psa-pc-remote[4135]: handlers_stderr: DEFER
May 23 23:02:36 srv1 psa-pc-remote[4135]: DEFER during call 'grey' handler
May 23 23:02:36 srv1 psa-pc-remote[4135]: Message aborted.
May 23 23:02:36 srv1 postfix/cleanup[26112]: 11635A02BF: milter-reject: DATA from localhost[127.0.0.1]: 4.7.1 Service unavailable - try again later; from=<[email protected]> to=<[email protected]>

Was there any recent change? Looking at my logfiles, it seems that this issue already happened before upgrading from 17.8 to Obsidian...