That’s an interesting question!
First the High Level Overview For Beginners
OK, maybe first we should ask ‘Why do we care?’
IP stands for Internet Protocol. It’s part of the TCP/IP (Transmission Control Protocol / Internet Protocol) network protocol which is used, pretty much, by all computers connected to a network. By network I mean a [...]
Talking directly to sendmail.
You can use telnet to talk directly to sendmail. This allows you to create mail from a different account. Sendmail uses port 25 by default.
$ telnet your.mailserver.address.com 25
You should get an introductory message from sendmail.
> helo your.domain.com
Sendmail responds with address details and ‘pleased to meet you’
> mail from: person@address.mail.is.from.com
Sendmail should echo back [...]