[philipwhiuk]

As a former K9 Mail developer I will say that the Google extensions to IMAP for Labels and OAUTH (neither of which are standards) are a pain in the backside that no email platform would have dealt with were it not for the fact they are huge.

(I did a spike development for OAuth and a separate investigation into Labels when I had some free time).

So they are definitely not nice IMAP citizens.

Oh and then there's the issues with Labels that their own documentation apparently gets wrong...

[Avamander]

To be fair here, labels are a great feature and the default limitation of a letter existing in only a single folder is a dumb remnant of ancient times.

If it's still not standardized then the pitchforks are aimed in the wrong direction.