Mail Server Extension not Working with office Email

Hello,

I'm new to ThingWorx, and my current version is 8.4. For the mail alert purpose, I imported the Mailserver Extension (V3.5.1). I tested sending emails from a Gmail account to an office mail, and it was working fine.

However, I want to send mail from one office mail to another office mail.

I entered my company's SMTP server name and port, which was provided by the IT department, but I am still getting the error message "Couldn't connect to host, port: xxxxx.xxxx.com, 25; timeout 30000."
also i tested the SMTP Server with telnet cmd its returned 220, seems good.
 

Mail Account User: I inserted the dedicated office email for the alert.

Mail Account Password: I left it empty, and also tried with the actual password of the mail account.

How can I solve this issue? Experts, please help me.

Thanks,