In Account Settings > Server Settings for an account, you can check the boxes for "Check for new messages at startup" and "Automatically download new messages".

JoeH said

My old eudora email program automatically checked for and displayed new messages as soon as I started the program. How do I get Thunderbird to do that automatically?

Thanks for the reply.

I UNchecked the box that said: "Check for new messages at startup," but the messages are retrieved on startup anyway. There is no item "Automatically download new messages" on the Server Settings page in version T'bird 38.3.0.

David