Mail Server can receive but cannot send to external mails

setup:

• aws ec2 instance hosted mail server
• smtp is configured to use port 587

scenarios:

• receiving mail from internal (same domain mail) and external (other mail like yahoo or google mails) is ok
• sending mail to internal (same domain mail) is ok
• sending mail from to external (other mail like yahoo or google mails) is NOT ok

Right now I cannot figure out the issue but i confirmed that the port for smtp is configured to be open correctly.

You have to request them open mailing ports. To prevent spammers they block them by default no matter your own firewall those are open.

hi I have confirmed that port 587 is open though I also tested it is not restricted unlike port 25