How to change webmail type for all domains in Plesk?

Login to the server via RDP.

Dump the list of domains:

C:> plesk db -Ne "select name from domains" > C:domains.txt

Go to CLI directory:

C:> cd "%plesk_cli%"

Update all domains to use Horde:

C:> for /f "tokens=*" %d in ('type C:domains.txt') do plesk bin subscription_settings -u %d -webmail horde

Note: The available options are:
horde - Horde Webmail
mewebmail - MailEnable Webmail
smwebmail - SmarterMail Webmail.
none -  Without webmail.

Login to the server via SSH as root.

Create a file webmail.sh with below script to switch webmail for all domains to Horde:

# cat webmail.sh
#!/bin/bash
for d in `plesk db -Ne "select name from domains"`
do
plesk bin subscription_settings -u "$d" -webmail horde
done

Note: The available options are:
roundcube - RoundCube webmail
horde - Horde webmail 
sogo_sogo - SOGo webmail
none - Without webmail.

Change permissions:

# chmod +x webmail.sh

Execute script:

# ./webmail.sh