Symptoms

Horde showing error pear\pear\smtp../../../locale is not a directory

Cause

Locale folder was missing at location at

%plesk_dir%\\Webmail\\horde\\pear

%plesk_dir%\\Webmail\\horde\\pear\\pear

%plesk_dir%\\Webmail\\horde\\pear\\pear\\Horde

%plesk_dir%\\Webmail\\horde\\pear\\pear\\Horde\\smtp

Resolution

Create empty folder Locale in the following paths:

mkdir "%plesk_dir%\\Webmail\\horde\\pear\\Locale"
mkdir "%plesk_dir%\\Webmail\\horde\\pear\\pear\\Locale"
mkdir "%plesk_dir%\\Webmail\\horde\\pear\\pear\\Horde\\Locale"
mkdir "%plesk_dir%\\Webmail\\horde\\pear\\pear\\Horde\\smtp\\Locale"