Too many inbound emails blocked by RBL check

Hello Community,
in the meantime, we are receiving more and more complaints from our customers that too many emails are no longer arriving.
I have noticed that many previously problem-free and unblocked emails are blocked by RBLs.
After I removed the RBLs, all "correct" emails come through again.
This problem first occurred about four weeks ago.
I am wondering why the RBLs are suddenly sporadically rejecting emails that have been coming through flawlessly for years.
Has anyone else here encountered such a problem?

Concerns various SOPHSO XG and XGS models.

Best regards

Michael

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