Not a hellish suggestion this time :)
At the present time, to properly setup our email account in thunderbird, when it is for a virtualmin-created account, we have to google for virtualmin documentation and proceed to the comments below that ( https://www.virtualmin.com/documentation/email/pop-and-imap ), read carefully the "Edit Users" page of our administration, and perform some rule of thumb most likely guess.
A simple suggestion, that in the Edit Users > email username > part of the admin, there is an additional section summarizing the information required to add in our email client.
With just - username - password (shown upon additional click in a popounder, as in other virtualmin pages) - server host name and port for pop3 - server host name and port for imap - which SSL option to choose (typically there's the choice between starttls and SSL/TLS, I know it's always the latter, but it ought to be precised as long as mail clients provide a choice)
I know it's not much, but at the present time, it takes some googling and careful copy-pasting to gather the info. To have it summarized for us in the place where it's most likely to be found already would make things more user-friendly :)
(Also, maybe just maybe : add somewhere an option to disallow non-ssl-secured email transmission, this way when a hired admin sets it up for a customer, the customer who doesn't know which port and SSL method to choose doesn't have the temptation to let everything transferred in the clear over the web, but that's another topic.)