I have just setup a new domain with MIAB. I used Custom DNS to set an A record for a website hosted elsewhere. The website is loading fine.
I have 1 e-mail address setup on the domain. I used Thunderbird to send an e-mail from this account and it worked fine.
When replying to that e-mail in Thunderbird I get the following message:
An error occurred while sending mail. The mail server responded:
Requested action not taken: mailbox unavailable or not local.
Please check the message recipient “firstname.lastname@example.org” and try again.
I have “checked the status page, re-ran setup, and rebooted the box”