You do not need rules 6 or 15 in your image as anything not specifically allowed will be denied automatically by the Endian firewall.
To troubleshoot what is happening start from the beginning;
Disable all outbound firewall rules and apply, turn on 'Log accepted outgoing connections' on Firewall > Outgoing Traffic screen (also check outgoing firewall is enabled
)
Now open the firewall log, Logs > Firewall Live Log
Try to telnet to an external SMTP server and check the firewall logs, you should see an entry like;
FORWARD:DROP TCP (br0) ,<pc ip>:55198 -> <server ip>:25 (eth3)
Now start enabling your outgoing firewall rules ONE at a time and try connecting to the external SMTP after every change, this will allow you to see which rule is allowing your outbound SMTP connection.
Hope this helps.