People using protonmail service may be unable to contact [banned mixer] but it's the same with other mixers, even the most famous one.
The message is rejected under suspicion of spam
That's why post #572 wasn't able to email them, and I'm sure post #573 is also using protonmail
example below
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message/delivery-status
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Reporting-MTA: dns; mail-41113.protonmail.ch
X-Postfix-Queue-ID: 4KCh5q4p2Zz4wwbp
X-Postfix-Sender: rfc822;
[email protected]Arrival-Date: Tue, 8 Mar 2022 16:45:35 +0000 (UTC)
Final-Recipient: rfc822; support@[banned mixer]
Original-Recipient: rfc822;support@[banned mixer]
Action: failed
Status: 5.7.1
Remote-MTA: dns; mx.yandex.net
Diagnostic-Code: smtp; 554 5.7.1 [1] Message rejected under suspicion of SPAM;
https://ya.cc/1IrBc azertyuiopqsdfghjklmwxcvbn
If you switch to another service, the email will be sent and received correctly as it should be