Possible account lockout. Not able to send emails

Possible account lockout. Not able to send emails

Hi,

I had a working email system for our account however for reasons still unknown i am not sure why the sending is not working and only the receive is working.  I have checked the blocked account, however dint see anything there. Can you please help me in this investigation. 

The only suspicion is a option clicked by our developer to send some alerts outbound and i am thinking that has caused some issue. I have disabled this option now.

Please advice.

Thanks,
G