Outlook 365 desktop not recieving Mail

I had an occation today to look at a machine that would not receive mail. Outlook had two mail accounts the primary and a second one.

    I checked all the settings and could not find any reason for no mail going to the primary account. I closed outlook down and opened the mail in the control panel. 

    A quick glance gave me no clues as everything looked correct, then i noticed that the primary email was not set as primary in the in the data section of the setup. I corrected this and mail started to arrive, not something i would have thought possibe.

Surly this is a Microsoft feature that is not required.