Keep in mind that Hetzner has a rather lax (non-existing?) policy when it comes to stopping outbound spam, so make sure to check that IPs you get from them are not on MX blacklists. To clarify - saying this as someone who was forced to blacklist their IPs on more than one occassion, not as someone who ran into tainted IPs as their customer.
The only organization that caused issues is Microsoft / Outlook.com, but they seem to block every IP address by default. I was able to unblock myself by filling out a form and waiting a few hours for all my servers so far.