I have two questions, I would really appreciate if someone could help me.
Q1: I am getting some emails rejected with a message saying "Sender verify failed" although the same users already sent emails to my exchange users and it was successfully received.
I noticed that the IP address which sent the successful email is different from the rejected ones although its not blacklisted by anything.
Q2: How is it possible to save emails that have been rejected so I could release them later if they are not spam/virus ?
R2: not possible when email are rejected at stage1.
To do what you want to do, you'll need to uncheck every rbl at smtp stage, also uncheck sender verify, SPF and almost anything on this page.
Then check all the rbl that you removed from SMTP to enable them in antispam/pre-rbl.
The load will increase on your MailCleaner, and many spams should pass through, I don't advise you to do this.