I typically don't like getting fobbed off, and certainly not after such a short answer.
I contacted them back and clearly pointed out that Mailbird does run in WINE, although a 2017 version, but still runs. I also mentioned that when they upgraded to .net 4.72 something causes the error (about 2 years ago), and although it doesn't flag in windows, it could. I asked politely to be put in contact with a developer who might be able to shed some light on this.
What I got back within 15 minutes was the best answer I've had so far:
Thank you for your reply. Our CTO worked in the past with some users to try and fix the issues with launching Mailbird on WINE, but new ones kept appearing as soon as they rectified current ones at that time. Mailbird does not work on Wine or any other Linux emulator as far as we know - at least the newest version and our development team are fully focused on work at Mac OS version of Mailbird at the moment. Once we have MacOS version there we may be able to release Mailbird for Linux as porting to Linux would be possible then.
They don't go into specifics, but I sent back asking when this WINE activity was, as WINE development recently has been at a substantially fast rate than it has ever been, and I also asked if the "CTO" would be interested in revisiting the Mailbird in WINE.
I didn't stop though, and through a lot of hoop jumping:
Yep - that's the latest version of Mailbird running right there, but crashes if you add new email accounts when fully installed (the mail server search is where it faults out with memory error)
I relayed this to Mailbird support and see what they come back with this time.
So how it was done:
> 32 Bit wine prefix, install .net 4, then .net 4.72 then VC2015-2019 (dotnet 4 and VC through winetricks, 4.72 via installer package)
> Install Mailbird 188.8.131.52 (found online free through respectable source), don't startup after install, don't update either
> Edit json file as before removing "no" entry (the es-us entry not here yet)
> Start Mailbird, and add an account (tried outlook only as GMail Auth out of date, and yahoo similar issue) - there are issues with some dialogs with this version.
> Goto settings, then updates, check for updates now - should download latest and install.
> It will try to reboot Mailbird, and fails, just close all windows.
> Re-edit json file removing the "no" and "es-us" entries
> Start Mailbird up.
Theres plenty of fixme flags in the console which some brighter people than I might be able to point out a solution to before I wake up tomorrow, and adding another email at this point crashes out with the usual memory error - shame can't add more emails in 2.4 without more hoop jumping (disabling auth stuff in Gmail and Yahoo etc.)
NOTE: did not test any built in apps yet (FB and messenger etc.), but assume as 3rd party integrations they might work OK - will play more tomorrow.