We had a need to install the SMTP server for some application but we want to change the default Mail directories path:
Unfortunately you can't just do it from IIS management console, for modifying the default paths you need metabase explorer.
However you can change the Badmail directory from IIS console: (right click smtp server --> properties -->Messages Tab)
modify it & restart the SMTP service for changes to take effect.
For other directories:
download & install the IIS Metabase explorer from the following link
Follow the wizard & choose custom installation
Just select the Metabase Explorer & finish the wizard.
Launch Metabase Explorer
Navigate to LM > SmtpSvc > 1 and change the directory paths
Restart the SMTP service & you will notice new paths gets created.
Just follow the steps mentioned above if you are in same situation.