Problem with Sending Service

Hello,
after it came to my attention that the double optin confirmation emails seem to have stopped being sent, I noticed that there are problems with the sending service. A month ago I was sending newsletters without any problems. Initially, there were no errors displayed in the status. After I tried to send a test newsletter, the following error message is now displayed:
The MailPoet Sending Service has been temporarily suspended on your website due to degraded email deliverability. Please contact our support team to resolve this issue.
I have no idea what is causing this and would appreciate any help.

Thank you very much.

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