SymptomsParallels Plesk Panel version 9.5 is installed on the server. Postfix is used as the mail server.
It is not possible to send mail from the server with the authorized user if greylisting spam protection is enabled on the server (Settings -> Spam Filter Settings -> option "Switch on server-wide greylisting spam protection" is enabled).
The error message "451 mail server temporary failed" is received when a message is sent out from the server.
Also, the following details can be found in the mail log $PRODUCT_ROOT_D/var/log/maillog:
Jun 18 14:19:45 ct greylisting filter: Starting greylisting filter...
Jun 18 14:19:45 ct before-queue: handlers_stderr: DEFER
Jun 18 14:19:45 ct before-queue: call_handlers: DEFER during call '/opt/psa/handlers/info/05-grey-cLDto9/executable' handler
Jun 18 14:19:45 ct before-queue: call_handlers: stop call handlers from dir '/opt/psa/handlers/before-queue/global'
Jun 18 14:19:52 ct postfix/smtpd: lost connection after UNKNOWN from localhost.localdomain[127.0.0.1]
ResolutionThis problem has been fixed in Parallels Plesk Panel since version 9.5.4.
The hotfix for older versions is attached. To install the hotfix, download the attached archive and unpack it with tar -zxf. In the resulting directory, find the postfix-queue file that is appropriate to your operating system and architecture. The archive contains a fixed binary for all operating systems supported by Parallels Plesk Panel 9.5.
Stop mail service with this command:
~# /usr/local/psa/admin/sbin/mailmng --stop-service
Replace the existing postfix-queue file with the one you have found. The location is defined by the Plesk variable $PLESK_LIBEXEC_DIR. It may be /usr/lib/plesk-9.0/, /usr/lib64/plesk-9.0/, or /usr/local/libexec/plesk-9.0, according to your operating system and architecture. Refer to this article to help you define the variable: http://kb.sp.parallels.com/en/5794
Please remember to correct the ownership and permissions for the replaced binary file. These should be set as mhandlers-user:popuser, 550. You may correct the permissions with the commands chown and chmod. For example, for CentOS5 32bit:
~# chown mhandlers-user:popuser /usr/lib/plesk-9.0/postfix-queue
~# chmod 550 /usr/lib/plesk-9.0/postfix-queue
After installing the hotfix, please remember to start mail service using the following command:
~# /usr/local/psa/admin/sbin/mailmng --start-service
Please read article #8083 to learn the hotfix installation procedure.