Up to a certain degree one can interpret the folders as tags. I think fastmail does it that way, iirc. Edit: Checked it: Yes, they treat folders as labels/tags

Up to a certain degree one can interpret the folders as tags. I think fastmail does it that way, iirc. Edit: Checked it: Yes, they treat folders as labels/tags, i.e., they simply copy the mail into all folders/labels/tags. See: https://www.fastmail.help/hc/en-us/articles/1500000278282 https://www.fastmail.help/hc/en-us/articles/1500000278282