AWS - how to use google SMTP - open port 587

 https://stackoverflow.com/questions/45036620/how-do-i-use-gmail-smtp-with-port-587-on-aws-ec2

you need to set your instance inbound rules for coming mail (need to open TCP port 587, and allow source of request from all IP address (0.0.0.0/0 for IPV4)

After that, you can send email using 587 SMTP port from AWS EC2.

* outBound is always allowed

https://stackoverflow.com/questions/44234374/aws-what-does-0-0-0-0-0-and-0-mean

0.0.0.0/0,::/0 - Means source can be any ip address, means from any system request is accepted, 0.0.0.0/0 represents ipv4 and ::/0 represents ipv6. To know CIDR (Classless Inter-Domain Routing) representation see this video