Email failed to send / service is currently unavailable

When trying to publish and send a post to my 72 members, I keep getting the message:

Uh-oh. Your post has been published but the email failed to send.
Email service is currently unavailable - please try again
Please verify your email settings if the error persists.

I’m running Ghost 5.23.0, was happening in the previous version as well
Ubuntu 20.04.4 LTS on a DigitalOcean Ghost Droplet
Mailgun Flex plan

I haven’t changed any of the setting that worked previously, and as far as I can tell in my mailgun account there’s no suspension or probation (which was the issue in most other similar cases I found on the forum). In my mailgun logs I can see recently sent emails to new subscribers and the successful test email I sent myself to preview the post, it just won’t work for the newsletter.

You’ll need to look in your logs and/or inspect the error_data field in the emails table in your DB to get a more detailed error message, that should tell you what is wrong.

Thanks for the help! According to the logs (after I tried again and it failed), the problem is on Mailgun’s side: “Mailgun Error 420: Domain is not allowed to send: recipient limit exceeded, try again after Wed, 23 Nov 2022 01:51:19 UTC”

I reached out to them for assistance but it’s weird because like I said there aren’t any restrictions listed on my account.