By default a client can’t upload files in plesk file manager larger then ~30MB . Unfortunately we have to let them upload bigger files because they like to use the  archive “uncompress” feature from file manager.
The error received in plesk is:
HTTP Error 404.13 – Not Found
The request filtering module is configured to deny a request [...]

For Parallels Plesk Panel version 7.x, 8.x:
Server -> Certificates -> Add New Certificate
For Parallels Plesk Panel version 9.x:
Settings -> SSL Certificates -> Add SSL Certificate
Fill in required preferences and click button {Self-Signed}
New self-signed SSL certificate will be created in server certificate repository.
To assign this SSL certificate for securing your Parallels Plesk [...]

Error log contains:
[emerg] (28)No space left on device: Couldn’t create accept lock
or
[crit] (28)No space left on device: mod_rewrite: could not [...]

Copy backup to plesk9 server and run:
/usr/local/psa/bin/pre9-backup-convert -v convert -d /var/lib/psa/dumps/  /root/plesk8-backup-file
then go to plesk 9 panel and restore the backup from the client and/or precreated domain.

step1:-
in Add Script Map dialog enter:
Request path: *.wgx
Executable: C:\Windows\Microsoft.NET\Framework\v2.0.50727\aspnet_isapi.dll
Name: VisualWebGUI-Page
Then click Request Restrictions…
Clear Checkbox: Invoke handler only if request is mapped to:
Click OK
Click OK again on Add Script Map
Step2:-
Change the application pool to classic.net apppool at basicsettings tab in under Actions menu.
Step3:-
give iis_iusers read permissions for web.config

when I try to implement other local delivery software for e.g. I need to modify .qmail file when a new email account is created/updated via plesk . if you just edit .qmail it will be rewrite on any email account update from plesk and same for new accounts you have to provision this shit somehow.
for [...]

PHP mail() and SMTP Authentication
Part of what makes the PHP mail() function is so simple is its lack of flexibility. Most importantly and frustratingly, the stock mail() does not usually allow you to use the SMTP server of your choice, and it does not support SMTP authentication, required by many a mail server today, at [...]

It happened that webmail from plesk windows just opened a page with error 503 , service unavailable. In our case it was horde webmail with plesk 8.6  IIS7 on windows 2008. Restarting whole IIS did not help.
Unfortunately I did not find too many docs related to it so find out from Parallels that webmail is [...]

Plesk ProFTPd sever has compiled-in mod_tls.c module for SSL support ans SSL support can be configured in /etc/proftpd.conf for example in the following way:

<IfModule mod_tls.c>
TLSEngine on
TLSLog /var/log/tls.log
TLSProtocol SSLv23
# Are clients required to use FTP over TLS?
TLSRequired off
# Server’s certificate
TLSRSACertificateFile /usr/local/psa/admin/conf/httpsd.pem
TLSRSACertificateKeyFile /usr/local/psa/admin/conf/httpsd.pem
# Authenticate clients that want to use FTP over TLS?
TLSVerifyClient off
# Allow SSL/TLS renegotiations when [...]

To configure PEAR bundled with PHP the following steps need to be completed:
1. Launch command prompt.
2. CD “%plesk_dir%Additional\Php\”.
Note: The folder can be different – e.g. in case of using PHP5.
3. Execute go-pear.bat and follow the on-screen instructions.
4. Add the path to the newly created pear.bat file into the PATH system variable after installation and reboot [...]