Odd symbol in Mailboxes column--Lazy Z

I added a second Inbox for a new email account for a business I work with. Now I see a symbol to the right of the mailbox that looks like a "lazy Z," or a Z rotated 90 degrees counter clockwise. It is in a gray circle. It also shows up in the main Inbox line to the right of "Inbox." Anyone know what this symbol means? I cannot find any info. Thanks.