Function open_mailbox 

fn open_mailbox(
    store: &dyn Store,
    account: Account,
    grant: &Grant,
    address: &str,
    before: Option<&str>,
    taken: &[String],
    test: impl Fn(&Account) -> Result<(), SyncError>,
) -> Result<(Account, Option<String>), SyncError>

The mailbox tried with the grant just kept under address, before anything else is kept: as the address; refused there (the token refused, or IMAP closed), as the login Microsoft’s page signed in, once, the grant moved there first, unless another account already uses it. Comes back with the account and, when it opened only under that other login (and the account did not already sign in as it, before), that login, for the person’s Yes. Nothing kept when it does not open.