Letterbox: what it reads, writes and never does.

What it reads

• It reads your mail, profile and calendar, and moves or drafts only when you approve.
• Revisions read from attachment names.

What it writes

• Unsent reply drafts waiting in Drafts for you to edit.
• Drafts wait in your Drafts folder. You read them, change them and press send.

Microsoft permissions

Letterbox asks for these, and has no permission to send mail:

• ReadItem (Outlook add-in manifest): read the Outlook message you have selected
• User.Read (delegated): identify the signed-in person
• Mail.ReadWrite (delegated): read admitted mail and folders, save unsent drafts, and file or undo approved moves. Microsoft's grant also allows deletion; Letterbox's own guards forbid deleting mail
• Calendars.ReadWrite (delegated): prepare meetings and create tentative holds you approve

Microsoft marks all three delegated permissions as not needing admin consent, but your tenant's own consent policy can still require an administrator.

These are today's lists. Microsoft's own consent screen shows the exact request when an administrator approves.

What it never does

• It cannot send mail, and it never deletes your mail.