I have been trying to get the pop3 activities working on UiPath on an AWS server. I have put in the username, password and hostname as webmail.server.co.uk but it seems to time out. I've tried both https and leaving that out.
I think you need to open port on your VPS as that is required to connect to the server. Also, you need to make sure that you are using the right type of authentication and the right type of connection. Doing this should resolve your issue.