I am facing a strange problem. I have configured some users to use their mail box from their mobile devices and outlook using POP3 and SMTP connection. The problem is that they can receive emails but they are not able to send emails. Whenever they send an email it goes to Outbox with a message status "Failed". This problem occurs with only some users others are able to send and receive perfectly without any error.
We have domain, Windows Server 2008 and Exchange Server 2010.
I have tried by changing the ports an security layers but no success.
Please help guys...