Banned 25 port after deploy Strapi

Hi all!
After deploying strapi on the server I got a port 25 ban for spamming. I got this response
“Please align the mail server’s HELO/EHLO ‘’ with proper DNS (forward and reverse) values.
Current rDNS:”.

This is terrible. Has anyone encountered something like this? How can I make sure this problem doesn’t happen again?

Thanks for the reply!