Additional testing requested, as I can only really test this with Gmail.

Pre-built eopkg files for your convenience (you need both as libytnef is a new dependency)

sudo eopkg install https://solus.reillybrogan.com:8443/geary/libytnef-2.0-1-1-x86_64.eopkg https://solus.reillybrogan.com:8443/geary/geary-40.0-29-1-x86_64.eopkg

PR to deprecate gmime26 packages now that Geary no longer needs them: https://github.com/getsolus/solus-sc/pull/132

I tested it with my account at a local e-mail provider (receiving, browsing, viewing, sending e-mails). While it did work in the end, it seemed remarkably unstable. The program crashed every time I added the account (the first two time losing the settings, the third time was the charm). Also it wouldn't launch at first, with a gschema settings error, until I did a sudo usysconf run -f

Now I've never used geary before, so this might be normal, but as a naive new user it seemed weird ?

In D12984#221166, @Staudey wrote:

I tested it with my account at a local e-mail provider (receiving, browsing, viewing, sending e-mails). While it did work in the end, it seemed remarkably unstable. The program crashed every time I added the account (the first two time losing the settings, the third time was the charm). Also it wouldn't launch at first, with a gschema settings error, until I did a sudo usysconf run -f

Now I've never used geary before, so this might be normal, but as a naive new user it seemed weird ?

What DE did you try it in?

Ah, sorry, that was on Budgie. I will do some more testing later to get to the bottom of it, or at least produce some logs, error codes, etc. Those were just the results of a quick one.

So, either something about today's updates coincidentally fixed my issues, or I had some old configs before from a much earlier test of geary, but after cleaning everything up and reinstalling it seems to work perfectly fine for me now. Sorry for the false alarm!