Email are queued but the spool is empty

Your software
My Mautic version is: 4.10
My PHP version is: 7.4.23
My Database type and version is: mysqlnd 7.4.23

Your problem
My problem is: When I want to send a newsletter (channel/emails) the emails are staying under “Queued” but the /var/spool is staying empty.

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Under email settings
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Is there something I can do?

Run the swiftmailer:email:send cron