archive/archive location fields are sometimes required for emails
A U.S. researcher asked me to pass this on: emails are now sometimes stored in printed form in folders, just like regular manuscripts. So it would be great to add Archive and Loc. in Archive fields to the email item type in Zotero
Depending on how you look at it, the email item type was either a mistake or is underdeveloped, but I don't think it's advisable to use in its current form.