Email unable to sent using smtp option

[pakogah]

I am still using WHMCS 3.6.1, and I use SMTP to sent email from WHMCS to all clients, but somehow email didn't sent to clients. I have check and double check my smtp server, user dan pass configuration. they all correct. I even test it using telnet to myserver port 25.

 

But somehow when I choose php mail, whmcs can sent email to clients. I am not prefer to use php mail and want to use smtp. is there any way to check what went wrong and how to fix it?

 

thanks.

 

ps: is it upgrading to ver 3.7.1 will solve my problem??