I've enabled popb4smtp in my mail server. It's holding the successful pop/imap logged in IP in the database. I've disabled "smtpd_sender_login_maps = mysql:/etc/postfix/mysql_sender_login_maps.cf" and remove "reject_sender_login_mismatch" from main.cf. While trying to send email I'm getting this error:

May 17 09:07:25 mail postfix/smtpd[6371]: connect from unknown[117.58.246.10]
May 17 09:07:27 mail postfix/smtpd[6371]: NOQUEUE: reject: RCPT from unknown[117.58.246.10]: 554 5.7.1 <unknown[117.58.246.10]>: Client host rejected: Access denied; from=<test@example.com> to=<test@test.com> proto=ESMTP helo=<[10.110.1.11]>

Is this because of the IP 117.58.246.10 don't have a dns record? How can I sending email from this type of Ip which don't have dns entry?. But if I enable SMTP auth I can send email form this same ip. Another thing is I can connect to port 587 from the email client to send email but can't connect to port 25.

Thank you.

I am not sure how the pop-before-smtp works, but apparently it is linked to DNS. You didn't mention what you are using for a POP/IMAP server, but my first suggestion would be to try using SASL authentication instead. Postfix supports it via either Dovecot or Cyrus add ons, with Dovecot being much easier to configure.

As far as not being able to connect on port 25, make sure your application is listening on port 25 and that you are not blocking it in a firewall. If you are still having problems, then there is a chance that your ISP is blocking this port, which is becoming too common.