I have a similar issue with Outlook:Mac 2011. The status bar keeps showing 'Downloading attachments0/1' then 'Sync pending for this folder'. It just keeps cycling, about once a second and is very annoying. Format a usb for mac os x.

Long story long, Apple use to have a utility that would allow syncing between outlook 2011 and iphones called isync (which is why there’s so much confusion on this issue). IPhone syncing is definitely supported in outlook for PC, but definitely not for mac. It was discontinued in Mavericks and El Capitan for an unknown reason. There has been no solid replacement for the software and the current apple position on syncing with outlook for mac is no support whatsoever. Microsoft’s position on the issue is no support. And, gmail’s position on the issue is no support.