Moving a message / thread from mailbox_1@tld_1.com to another mailbox_2@tld_2.com is not possible.
Proposed Solution
It should be possible, to move messages from one mailbox to another. At the moment it’s only possible to move messages / threads into subfolder of the same mailbox. If you have multiple mailboxes with different TLDs you can not move the messages with mailspring client
Having the same problem. I switched from having Gmail collect everything to Mailspring’s unified mailbox and now I am stuck with not being able to move incoming emails from one mailbox to the other.
Any solution four years later?