Outlook mobile app duplicate meeting invitations

%3CLINGO-SUB%20id%3D%22lingo-sub-3366324%22%20slang%3D%22en-US%22%3EOutlook%20mobile%20app%20duplicate%20meeting%20invitations%3C%2FLINGO-SUB%3E%3CLINGO-BODY%20id%3D%22lingo-body-3366324%22%20slang%3D%22en-US%22%3E%3CP%3EOutlook%20app%20on%20mobile%20devices%20(both%20Apple%20and%20Android)%20sends%20duplicate%20meeting%20invitations%20every%20time%2C%20every%20user.%20I%20cannot%20find%20the%20reason.%20It%20started%20to%20happen%20recently.%20I%20have%20duplicate%20items%20in%20%22Sent%22%20and%20recipient%20gets%20duplicate%20messages%2C%20and%20there%20are%20duplicate%20calendar%20entries.%20Messages%20headers%20differ%3A%20one%20has%20message%20id%20ending%20with%20%22namprd06.prod.outlook.com%22%20and%20the%20other%20with%20my%20domain%20name.%20Other%20apps%20do%20not%20have%20this%20problem%20like%20iPhone%20native%20Calendar%20app%20sends%20invitations%20correctly.%20I%20use%20Exchange%202016%20CU20%20Version%2015.1%20(Build%202242.4).%20Planning%20to%20upgrade%20to%20latest%20soon.%3C%2FP%3E%3C%2FLINGO-BODY%3E%3CLINGO-LABS%20id%3D%22lingo-labs-3366324%22%20slang%3D%22en-US%22%3E%3CLINGO-LABEL%3E2016%3C%2FLINGO-LABEL%3E%3CLINGO-LABEL%3EExchange%20Server%3C%2FLINGO-LABEL%3E%3CLINGO-LABEL%3EOutlook%20mobile%3C%2FLINGO-LABEL%3E%3C%2FLINGO-LABS%3E
Occasional Visitor

Outlook app on mobile devices (both Apple and Android) sends duplicate meeting invitations every time, every user. I cannot find the reason. It started to happen recently. I have duplicate items in "Sent" and recipient gets duplicate messages, and there are duplicate calendar entries. Messages headers differ: one has message id ending with "namprd06.prod.outlook.com" and the other with my domain name. Other apps do not have this problem like iPhone native Calendar app sends invitations correctly. I use Exchange 2016 CU20 Version 15.1 (Build 2242.4). Planning to upgrade to latest soon.

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