Email failed to send - please verify your email settings 📧 / Email service is currently unavailable - please try again

the problem is finally solved, the first error was due to the version 3.32 of Ghost now fixed.
The second problem was due to Mailgun who had restricted my account permissions, they finally answered me and re-enabled my account.
It is not clear why it was limited.

Regarding Ghost, it would be useful to see these kinds of errors in the error log file instead of the production one