I see. Maybe that's because mailtrain adds unsubscribe headers in the email header etc. I don't really know of any other bulk mailer software. Are you able to contact the support of turbo mailer and ask them if they support STARTLS at all?
That seemed to solve it, even if a server reboot did not solve it. I also got a mail, that this was also visible from other mail-servers (not just from my mail client), as I use DANE for certificate pinning.
I had the same issue. And the same fix. A reboot didn't work, a service restart did the trick. Thanks!
@girish This is an interesting observation. I was just looking to see if this was a real security threat or not, and I suppose it isn't but can offer a bit more privacy using the wildcard approach. Any particular reason why the Let's Encrypt wildcard support can't be done through the actual Cloudron wildcard DNS approach? Is there a way to support this? I'd really like to take advantage of a smaller DNS provider which has some great monitoring features included, but it isn't supported via any API by Cloudron yet, so if I go that route I can only use the Wildcard option, but those don't actually allow for the wildcard certificates.
Edit: Nevermind, I see why in the docs: "Let's Encrypt only allows obtaining wildcard certificates using DNS automation. Cloudron will default to obtaining wildcard certificates when using one of the programmatic DNS API providers."
Are you hosting a custom domain on mailbox.org or do you have a @mailbox.org address? If it's the latter, mailbox is then not really an email relay. Generally, email relays are able to forward all addresses of a domain i.e email@example.com.