Laravel with iRedMail gateway timeout in aws ec2

I just migrated a laravel app to amazon ec2 server. I have 2 instancies, one with the laravel app and the other with the mail server (iRedMail).

The mail server seems to work since all the emails are sent/delivered correctly.

The problem is connecting the Laravel app with the mail server: here is my app/config/mail.php file

'driver'=> 'smtp',
'host'  => 'ns-XXX.awsdns-XX.net',
'port'  => '25',
'from'  => ['address'=>'info@example.com','name'=>'Info'],
'ecryption' => 'ssl',
'username' => 'info@example.com',
'password' => 'SecretPassword',
'sendmail' => '/usr/sbin/sendmail -bs',
'pretend'=>false

The mail server instance has permissions to smtp connections on port 25.

When I try to send an email through the Laravel app it occurs a 504 Gateway Time-out

I'm kinda new in sysadmin so I have no clue on what to check. Any tips will help, thanks! :)