Im running OSX 10.13.6
I have a range of email accounts setup in mac mail, mostly google apps for business gmail accounts and iCloud accounts.
I have 1 custom hosted IMAP / SMTP account which for some reason is showing a "square icon" (see below screenshot) in the sidebar for the sent mailbox. The inbox mailbox for this account works, but the sent doesn't.
Any ideas why this might be and what the square icons means ?