FIM email error 3

Hello Everyone, 

i'm getting this error when FIM tries to send an email, 

i'm gessing its an exchange issue but does anyone have an idea on how to solve it ?

below is the configuration i'm using

<add key="mailServer" value="smtp.xxx.net" />
    <add key="isExchange" value="0" />
    <add key="sendAsAddress" value="svc_PRO_FIM_PORTAL@xxx.com" />

thanks  !

Hitch Bardawil