But on the new computer TB refuses to send the emails. I've tried most of the suggestions to solve the problem but now I'm at my wit's end.

Hi there, I urgently need help with TB on my new computer (MacBook Air 2020). I've installed TB 78.6.1 there as I've done on my older MacBook (I didn't migrate the App since it didn't work due to a mistake in one of the subfolders - errormessage-nr. -35; so I just downloaded it from the internet). I looks pretty good since all messages come in and all subfolders are complete. The setting is just THE SAME as it is in TB 78.6.1 on my older computer (I've checked every single configuration option, not just the smtp) and there it works just flawlessly. But on the new computer TB refuses to send the emails. I've tried most of the suggestions to solve the problem but now I'm at my wit's end. After pressing the 'send'button it shows this: "Transaction failed Reject due to policy restrictions. For explanation visit https://postmaster.gmx.net/en/error-messages?ip=91.66.122.145&c=hi." How is this possible if at the same time TB works just great for the same Emailprovider (gmx) and -address on the other computer? Pretty much hope that somebody has an idea that helps. Thank you very much in advance! Salut, Sandra