Add "Papercut" to SMTP banner

[jorrit]

I wanted to test my remote mail server using the well known telnet method (HELO/MAIL FROM/RCPT TO/DATA). Although the server seemed to respond fine no mail was sent. It wasn't until much later that I realized that I had this server mapped to localhost in my hosts file, I was actually talking to Papercut.

I would like to request a feature where Papercut advertises the program name at the start of the SMTP session in the 220 line such that it is easier to recognize that the SMTP server is Papercut.

[Jaben]

Okay with me 👍