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SMTP -- an example

What you type is in bold type. You can get an SMTP connection by telnetting to port 25.

220 memoryhole.net ESMTP helo friend 250 memoryhole.net mail from: st.claus@north.pole 250 ok rcpt to: foo@bar.com 250 ok data 354 go ahead content goes here . 250 ok 1047595906 qp 9888 quit 221 memoryhole.net

Easy.

SMTP AUTH — an example

SMTP AUTH is more interesting. For the following examples, presume that the username is foo and the password is bar.

For AUTH PLAIN, the conversation looks something like this:

AUTH PLAIN 334 AGZvbwBiYXI= 235 2.0.0 OK Authenticated

That garbage in the middle is the base64-encoded string generated like so: printf "\0foo\0bar" | openssl base64

For AUTH LOGIN, the conversation looks something like this:

AUTH LOGIN 334 VXN1cm5hbWU6 Zm9v 334 UGFzc3dvcmQ6 YmFy 235 2.0.0 OK Authenticated

Again, that's just all base64-encoded, only rather than having nulls first like in the PLAIN example, LOGIN expects just the characters, without nulls, generated like so: printf 'foo' | openssl base64. Decoded, the above conversation looks like this:

AUTH LOGIN 334 Username: foo 334 Password: bar 235 2.0.0 OK Authenticated

An SSL connection can be made with the openssl program, like so:

openssl s_client -starttls smtp -connect host:port