[nicolaslem]

I believe that in email-land what you describe is usually referred to as labels rather than tags. Many email providers use labels under the hood for everything, Gmail being the most famous one. For instance the Inbox is just a collection of emails with the "new" label attached.

You can of course define your own labels, for example:

- https://fastmail.blog/productivity/fastmail-labels

- https://support.google.com/mail/answer/118708

Caveat, labels may be a bit clunky when using thrid-party clients and IMAP.

It is great that you have found a low-tech solution to a problem you have, but you may be reinventing the wheel a little.

[masukomi]

there's a key difference.

labels are applied _after_ the message is _received_. Their solution applies the tags _before_ the message is _sent_.

thus they're tagging the thread at the beginning of their interaction with it.