Issue

The Junk Mail settings in Outlook 2016 are not available when using Bowdoin mail. The option exists but you can not click the + or -.

Resolution

There is no resolution at this point. Microsoft does not support Junk mail settings in Outlook 2016 for Mac. Outlook 2016 for Mac does not support client-side junk email settings. Here's some information from one of Microsoft's blog posts about this issue:

The first item to understand is that there are two types of junk email filtering: sever-side and client-side. Server-side junk filtering takes place on the mail server (such as Exchange) as soon as email arrives in the mailbox.  Client-side junk filtering takes place on the client (such as Outlook & Outlook for Mac) when the email is downloaded from the server to the client.

Outlook 2016 for Mac does not provide any client-side junk mail protection for any type of account (Exchange, POP, or IMAP). Instead, it relies solely on the mail server to perform all junk email filtering. Emails are not scanned client-side by Outlook 2016 for Mac to determine if they are junk email. Exchange servers provide server-side junk mail filtering, and most popular email providers, such as Hotmail, Outlook.com, Gmail, and Yahoo, provide server-side junk mail filtering, making client-side Outlook junk filtering redundant.

It’s important to understand that junk mail filtering and blocked senders are not the same thing, although they are often used in conjunction. Junk filtering is when emails headers and content is scanned for characteristics that makes the email likely to be junk. When you add an email address to the Blocked Senders list, emails from that email address are always moved to the Junk E-Mail folder.

https://blogs.technet.microsoft.com/office_for_mac_support_team_blog/2015/06/19/junk-mail-in-outlook-for-mac-for-office-365/

You can, however, manage your safe-senders, block list and allowed list through Office.com. View the article linked on the left, under Related Articles, titled "How to manage what email is blocked by the spam filter"