apt install -y swaks
swaks --from sender@domain.com --to rcptuser@domain.com --auth-user myuser --auth-password "mypass" --server email-smtp.eu-west-1.amazonaws.com --tlsc
--tlsc, --tls-on-connect
Initiate a TLS connection immediately on connection. Following common convention, if this option is specified the default port changes from 25 to 465, though this can still be overridden with the --port option.