From one day to the other Outlook stalls for several minutes when it has received mail, with all accounts, so not one in particular.

After a couple of minutes I can resume using Outlook again, until a new mail arrives.

It is as if Outlook cannot be set or selected as front application for that period.

Already tried rebuilding identity, no solution.

Also tried disabling the 'group mails' option, no result either.  :-(

Outlook for Mac version: 14.6.1

Mac OS: Yosemite 10.10.5