mailbox.org reliability?
 

Does anybody have any experience in terms of mailbox.org uptime and whether there are any issues in terms of delivery to the main email providers (gmail, yahoo, outlook, etc)?

See this thread

Thanks, but most of the thread discusses other issues -- related to using own domain, UI etc. I didn't see any comments about emails from mailbox.org not delivered elsewhere, just potential issues with how delivery to them due to how they handle spam (hard reject).

Mailbox works good, I use it for some time now.
Maybe not important for you, but Mailbox.org runs also an XMPP server.