The mid-oughts battle over this in the international standardizations space is pretty fraught: https://en.wikipedia.org/wiki/Standardization_of_Office_Open...
And even now, even though there is a "standard" and schemas for, MS's apps mostly ignore them, or use undocumented extensions (as far as I'm aware), so it the whole thing was truly straight from MS's embrace/extend/extinguish playbook.
Primarily because there isn't a fully-functional equivalent.
Even more reason to switch.
The last time I checked, Thunerbird can't flag a contact for reminder, or set the same category for an email and a task?
The answer is no, not unless an absolutely crippled version is sufficient for your needs.
The mid-oughts battle over this in the international standardizations space is pretty fraught: https://en.wikipedia.org/wiki/Standardization_of_Office_Open...
And even now, even though there is a "standard" and schemas for, MS's apps mostly ignore them, or use undocumented extensions (as far as I'm aware), so it the whole thing was truly straight from MS's embrace/extend/extinguish playbook.