Your question seem quite broad. It's much easier to answer more specific questions.
Mail.dll's only requirements are :.net framework or .net core installed and working network connection. Please note that your app needs to have enough permissions to open socket connection to the email server.
IMAP and POP3 are standard protocols and Mail.dll supports both of them fully. It was tested against all major email providers like Gmail, Outlook, Yahoo, QQ and major server software like Exchange, Dovecot, hMailServer.
As always we strongly advise using IMAP instead of POP3 - it's simply easier to work with.
You can find many samples showing how to download emails, parse and process them here: