I just have came across the instant where my mail client was unable to connect the mail server so that I was asked to use the webmail but the webmail service for our mail server has not enabled the SSL certificate. All the email communication through our web mail will be held on http connection only instead of https. I know that the data transmission of our email communication in this situation will be unencrypted. However, I would like to know more in detail what are all impacts can be possible due to the data transmission on http protocol instead of https protocol for mail communication of this situation.

Thank you