Polymail respects the spam filtration and rules put in place by your email provider. Anything they detect as spam should be moved automatically to your Polymail spam folder.
If a spam email does make its way to your inbox, though, you can always mark it as spam from Polymail itself.
To do so on our Web and Desktop apps:
Using our ⌘J Popover feature, type Command + J to pull up the Command Center
Type either "mark" or "spam" to find the Mark as Spam command and click Enter when it appears:
You can do the same in our iOS app this way:
Click into the email you want to mark as spam
Click the three horizontal dots in the top right corner of the screen
Click "Mark as Spam" in red in the menu that appears: