AWS server port 25 blocked after few hours of server creation

I am running a EC2 large.t3 instance with CentOs.

My server Region is Ohio.

I have installed WHM and it is working fine.

When I created a server PORT 25 working fine. But after few hours port 25 gets blocked. Due to this I'm not ablw to send any email from my webmails.

Here is the snippet..

Just after server setup:

[root@ip-172-31-43-92 ~]# telnet
aspmx.l.google.com 25
Trying 172.217.214.26...
Connected to aspmx.l.google.com .
Escape character is '^]'.
220 mx.google.com ESMTP
n18si6406443jao.103 - gsmtp
quit
221 2.0.0 closing connection
n18si6406443jao.103 - gsmtp
Connection closed by foreign host.
[root@ip-172-31-43-92 ~]#`
After few hours and restart:

[root@ip-172-31-43-92 home]# telnet
aspmx.l.google.com 25
Trying 172.217.212.26...