One of my user have optonline account and i have configured his outlook. He can able to recieve email but can't send out. I have check with ISP if they are blocking the port and they said no.
I have tried telnet... telnet mail.optonline.net 25 ...it failed so that mean my firewall is blocking it. Optonline also told that i can use 587 secure port for them. Can you please advsie how can i open these ports. Should i even open 25 port or it's security risk. Thanks.