email is not being sent on host

The simple user signup activation email is not being sent when I put my
app on host, but works pretty fine on my dev machine.

I am using Gmail (with smtp_tls plugin of course) server to send
email...I have tried putting it on another host too but there it doesnt
work there too. And logs are clean. Pretty strange.

The logs being clean in production isn't strange at all.

Try setting config.log_level = :debug in environment.rb.