Under plesk account if domain webamail link shows blue screen or default plesk page.. then how can you fixed this..

Solution:
Login to your plesk server through root



[master@tunevps ~]$ sudo su - root

[master@tunevps ~]
[master@tunevps ~]cd /etc/psa/webmail/horde/conf.d/

[master@tunevps ~:/etc/psa/webmail/horde/conf.d]
(root)>ls -al | grep testvps.com
[master@tunevps ~:/etc/psa/webmail/horde/conf.d]
[master@tunevps ~] cp -a /etc/psa-webmail/horde/conf.d/tugawarsportfishing.com /etc/psa/webmail/horde/conf.d

[master@tunevps ~:/etc/psa/webmail/horde/conf.d]
[master@tunevps] service httpd stop
Stopping httpd: [ OK ]
[master@tunevps:/etc/psa/webmail/horde/conf.d]
[master@tunevps] service httpd start
Starting httpd: [ OK ]

This should be fixed your problem

====================================================================