Degraded email deliverability and Sending Service

Hello and good day,

I exported a contact list of my clients using mailpoet.
I imported the same list to another site, also owned by me, using mailpoet.

I tried to send a test newsletter but the sending stops and 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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