Hello,

I am a fan of nginx and I really like nginx mail proxy module. I'm having a problem between the authenticated account and the sender when using this module. For better understanding, please see my test below:

root@nginx:~# telnet xx.xx.xx.xx 25
Trying xx.xx.xx.xx ...
Connected to xx.xx.xx.xx .
Escape character is '^]'.
220 smtp.xxx.xxx ESMTP ready
ehlo mail.example.com
250-smtp. xxx.xxx
250 AUTH LOGIN
AUTH LOGIN
334 VXNlcm5hbWU6
xxxxxxxxxxxxxxxxxxxxxxxxxx
334 UGFzc3dvcmQ6
xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
235 2.0.0 OK
mail from: admin@gmail.com
250 OK <admin@gmail.com> Sender ok
rcpt to: admin@gmail.com
250 OK <admin@gmail.com> Recipient ok
data
354 Start mail input; end with <CRLF>.<CRLF>
test
test
.
250 OK
quit
221 Service closing transmission channel
Connection closed by foreign host.

As you have seen, after successful authentication, I can send email using any account and nginx skips checking if this account matches the previously authenticated account.
I want to write more code in the source code of the mail module in nginx to be able to check if this account matches the previously authenticated account, however I don't know C programming nor understand how functions in .c source code files work.

Currently my server is being used to spam emails a lot. So I would really appreciate it if you could give me some advice to fix my problem.

Thank you very much!