I can send mail to private server addresses (info@centos.com) but I cannot send mail to addresses like hotmail gmail. I have a static ip address in my office and I am a home user. I am not experimenting on the server. When I ask my service provider, they say there is no blocking of the 25 ports. Can you help me?
When I test it on mail-tester.com, no mail is received.
Spf records are important. So is ip reputation. Of you have none, Gmail is a pita. Use mxtools to make sure your not on blacklists, and check root mail (install mutt) to see responses from Gmail's servers.