If so, is it being verify through internet every time I use the program?
Is the license tied to my email/account that I can only use on one computer?
No, No and No. 
Cryptomator uses the crpytographic Public/Private-Key mechanism to check if the license is valid.
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Technically, it’s as @infeo mentioned. We wanted to make it as unobtrusive as possible.
Legally, the donation key is bound to one user that can be used on as many devices as you want.