To enable or disable receiving e-mails, click on your avatar, go to Settings,
and select Notifications.
Productive will send you e-mail notifications to remind you to track your time, unless you turn it off.
Read here about changing settings for Time reminders.
Productive will also send an e-mail when something happens on a project/deal/budget you're subscribed to.
Someone closed a task, or assigned you one, or mentioned you in a comment, or marked a deal as won... you'll be notified about everything you're keeping a track of.
If you want to turn it off, uncheck the checkmark next to E-mail notifications.