monterail-fulldark VS Mailspring-Sync

Thank you for this! Looks beautiful :) However I found that the linked theme has not been maintained for the last 4 years, so doesn't work for versions >= 68. There is another maintainer though that has taken over development here

At the thunderbird add-on page, the developer(conema) says, the missing themes (light and blue) will probably also be released as add-ons at some point:

I was hopeful that https://www.nylas.com/ would be the de-facto "adapter" placing a common API surface on top of the major providers and dragging them into a modern-API world. They even had an email client of their own as a proof of concept (forked by one of the original authors as https://github.com/Foundry376/Mailspring - and its reusable core https://github.com/Foundry376/Mailspring-Sync may be interesting to many here). But they've pivoted towards making their API only available behind B2B contracts and opaque pricing, and primarily used for corporate email monitoring and CRM use cases - perhaps because security and privacy considerations are nontrivial. I'm still rooting for them but it's a shadow of what it could have been.

MailSpring is either done to look at soon ... it's either very close to finalizing Bridge support or in fact done. It's not clear to me, there's a discussion in GitHub. Nice thing about MailSpring is that it has a Linux client (Postbox only has Mac and Windows).

Yeah that's what I found too.