What version RouterOS are you using?
Mine is under tools - email, and my email test was in my inbox first try. I am using ROS V6.5 and Linux with Sendmail as the smtp server. And the same router sends me a voltage readout for the last 24 hours every day.
I have in the past tried sending to my gmail account and it works also.
I tried to send through one of my servers that does not accept port 25 email, and I got a message in my log like this. It took a minute or so to show up in the log:
Dec/26/2013 18:08:07 system,e-mail,error Error sending email <test>: abnormal termination [timeout]