In SmarterMaill 4.3 and above, this can be controlled at the User's Inbox through Settings > My Settings > Compose. Set the Text Encoding to "Unicode (UTF-8)" ("Arabic (ISO)" might work too) and then try sending the email again. This will affect any outgoing mail after the settings are saved, existing messages will not be changed.
This is per user setting.
Rubal Jain
SmarterTools Reseller - Contact for new Licenses and Upgrdes
Helm Server Installation, Configurations, Troubleshooting
Windows Support
Helm Server, SmarterTool Servers Migrations, Moves, Restorations