Import/archive of same email from different sources results in orphan source entry

The source is stored using an index created from the hash of the full message, so any differences result in a different hash.

However the mbox summary record uses an index derived from elements of the message that are more likely to be the same for emails of different sources. The second email replaces the the entire mbox entry, thus losing the link to the first source entry.

This is quite different from the classic PonyMail behaviour and needs documentation if it cannot be fixed.

Start by tracing the import/archive handling for the source index and mbox summary record described in the issue, then reproduce two messages with the same summary key from different sources. Done means the first source link is retained, or the behavior and its difference from classic PonyMail are documented if it cannot be fixed.

Written by the indexing model from the issue text.