Notification email to internal smtp server failed

cannot send email via SMTP port 25 :

t=2020-10-08T06:08:01+0000 lvl=eror msg=“failed to send notification” logger=alerting.notifier uid= error=“Failed to send notification to email addresses:; dial tcp x.x.x.x:25: i/o timeout”

in our on premise exchange server and firewall, already allowed my VM (Azure) to access port 25 server exchange. how can i solve this issue ? your help is appreciated.