If you post about "334 VXNlcm5hbWU6" be aware what you are sharing / 2017-07-25

I saw someone post somewhere about problems with sending mail, with the complete session log. E-mail addresses were obfuscated, but there was a part of the session not obfuscated, which had far more interesting secrets than just e-mail addresses. It looked a bit like this:

250-HELP
250-AUTH LOGIN PLAIN
250-SIZE 157286400
250-8BITMIME
250 OK
AUTH LOGIN
334 VXNlcm5hbWU6
dXNlcm5hbWU=
334 UGFzc3dvcmQ6
cGFzc3dvcmQ=
235 ... authentication succeeded
RSET
250 OK

Those "random" letters and digits look a lot like base64, so to decode them:

$ echo "VXNlcm5hbWU6" | base64 -d ; echo
Username:
$ echo "dXNlcm5hbWU=" | base64 -d ; echo
username
$ echo "UGFzc3dvcmQ6" | base64 -d ; echo
Password:
$ echo "cGFzc3dvcmQ=" | base64 -d ; echo
password

So the random letters and digits are actually username and password, very interesting information. Searching for VXNlcm5hbWU6 gives me examples of usernames and passwords.