# Mail Tag Projection

This context describes a mailbox view that groups messages by plus-address tags while retaining one authoritative message and state.

## Language

**Source Maildir**:
The authoritative Maildir whose messages and shared state are exposed through tag folders.
_Avoid_: Source directory, original folder

**Plus tag**:
The complete suffix after the first `+` in a recipient address local-part. A plus tag identifies one flat tag folder.
_Avoid_: Label, category, nested tag

**Tag folder**:
A mailbox folder containing projections of every source message carrying its plus tag.
_Avoid_: Physical folder, copied mailbox

**Tag namespace**:
The separately mounted Dovecot namespace that contains all generated tag folders.
_Avoid_: Overlay, destination directory

**Message projection**:
An appearance of a source message in a tag folder. Multiple projections share the source message's state and lifetime.
_Avoid_: Copy, duplicate

**Mailbox hierarchy separator**:
The configured Dovecot namespace character that separates mailbox levels and therefore must be escaped when it occurs inside a flat plus tag.
_Avoid_: Maildir delimiter, tag separator