Email is not delivered. The following messages are shown in the
handlers_stderr: DEFER DEFER during call 'grey' handler Message aborted. milter-reject: DATA from mail.example.com[x.x.x.58]: 451 4.7.1 Service unavailable - try again later; from=<email@example.com> to=<firstname.lastname@example.org> proto=ESMTP helo=<email.example.com>
Handlers Filter before-queue for qmail started ... email@example.com firstname.lastname@example.org Starting greylisting filter... handlers_stderr: DEFER DEFER during call 'grey' handler
After a while, email finally arrives into the mailbox with the following entries in
Starting greylisting filter... handlers_stderr: SKIP SKIP during call 'grey' handler
This is an expected behavior of Greylisting that introduces a short delay before accepting mail: mail gets deferred for the first time, then gets delivered for the second attempt to send an email. In most cases, mail from a valid sender will be delivered within an hour, but depending on how the sending server is configured, it could be much longer.
Mail from a spammer, on the other hand, will be deferred for 1 time and mail sending will not be retried: spammers usually send mail in bulk to thousands of recipients and do not bother with resending. See Plesk Administrator Guide for more details.
Delay takes place because Greylisting verifies three components of message: IP, sender, recipient. Based on these components Greylisting determines whether it should issue a temporary reject code or accept the message.
To prevent delay, put required mailbox or the whole domain
*@example.com into White List in:
Tools and Settings > Spam Filter > White List
This way email from the white-listed senders will be accepted without passing through the greylisting check.
Alternatively, disable Greylisting spam protection on the whole server:
Tools and Settings > Spam Filter > Switch on server-wide greylisting spam protection
The following statuses can be seen in
maillog: DEFER, SKIP, REJECT
In terms of Greylisting
DEFER means 'try again later';
SKIP means 'allow delivery';
REJECT means that the sender IP is blacklisted globally.