Parallels released Plesk 9.2 with greylisting support in it, however, it appears that they didn’t implement it in the control panel and setting it up must be done via the command line.

• [How to] How to configure white list for Greylisting?

ie:

/usr/local/psa/bin/grey_listing –help | less

Usage: grey_listing command [options]

Available commands:
–update-mailname or -um <mail@domain>
updates the grey listing
configuration for existing mail user
–update-domain or -ud  <domain>   updates the grey listing configuration
for existing domain
–update-server or -u              updates the grey listing server-wide
settings
–info-mailname or -im <mail@domain>
retrieves grey listing settings for
given mailname
–info-domain or -id   <domain>    retrieves grey listing settings for
given domain
–info-server or -i                retrieves server wide grey listing
settings
–help or -h                       displays this help page
Available options:
-status            <on|off>        enable/disable grey listing. Used with
–update-domain or with
–update-server command
-personal-conf     <true|false>    allows or prohibits personal grey
listing configuration for users. Used
only with –update-server command.
-grey-interval     <number>        updates grey interval value (in
minutes). Used only with
–update-server command
-expire-interval   <number>        updates expire interval value (in
minutes). Used only with
–update-server command
-penalty-interval  <number>        updates penalty interval value (in
minutes). Used only with
–update-server command
-penalty-status    <true|false>    enable/disable penalties for server.
Used only with –update-server command
-blacklist <add|del>:<pattern1[,pattern2]>;…
adds, deletes e-mail(s) pattern of
black list shared with spamassassin.
Used with –update-mailname or with
–update-server command
-whitelist <add|del>:<pattern1[,pattern2]>;…
adds, deletes e-mail(s) pattern of
white list shared with spamassassin.
Used with –update-mailname or with
–update-server command
-domains-whitelist <add|del>:<pattern1[,pattern2]>;…
adds, deletes domains pattern of
white list. Used only with
–update-server command
-domains-blacklist <add|del>:<pattern1[,pattern2]>;…
adds, deletes domains pattern of
black list. Used only with
–update-server command

URL:

• Plesk 9.2.1 greylisting not working