On first start WebMail creates in your home directory files:
If file mbox does not exist it is not created. However if it exists , the letters from /var/mail/user are moved to this folder. WebMail refers to it as INBOX. (similarily as Pine).
If you decide to use WebMail do not collect a lot of messges in your INBOX - Webmail becomes very slow.
You will be connected to IM PAN Webmail with a secure connection and you will have to accept the certificate of this site.
Problems with certificate ?
This certicicate is temporary, it will be replaced soon by more faithfull.