Very strange
I have now also enabled the WBXML logging on user level.
I made the following observation:
ActiveSync to Outlook (empty mail again):
27/11/2018 15:25:34 [52758] [DEBUG] LoopDetection->Detect(): folderid:'U8f1e2' uuid:'cd79093a-380a-407e-9beb-0371571d87d4' counter:'57' max:'512' queued:'1'
27/11/2018 15:25:34 [52758] [DEBUG] PHPWrapper->ImportMessageChange(): Getting message from MAPIProvider, sourcekey: '0ee843f10bcd460cb98d440c5eed76bd86fa00000000', parentsourcekey: '0ee843f10bcd460cb98d440c5eed76bd3a0000000000', entryid: '0000000099811161ecb746208ffd513c7d44f03d0100000005000000d20b9abe70c440eeae813a597af7b25400000000'
27/11/2018 15:25:34 [52758] [DEBUG] BodyPreference types: 4
27/11/2018 15:25:34 [52758] [DEBUG] GetBodyPreferenceBestMatch: 4
27/11/2018 15:25:34 [52758] [DEBUG] bpo: truncation size:'0', allornone:'1', preview:'0'
27/11/2018 15:25:34 [52758] [ERROR] MAPIProvider->imtoinet(): got no stream or content from mapi_inetmapi_imtoinet()
27/11/2018 15:25:34 [52758] [WBXML] O <Perform>
27/11/2018 15:25:34 [52758] [WBXML] O <Add>
27/11/2018 15:25:34 [52758] [WBXML] O <ServerEntryId>
27/11/2018 15:25:34 [52758] [WBXML] O U8f1e2:0ee843f10bcd460cb98d440c5eed76bd86fa00000000
27/11/2018 15:25:34 [52758] [WBXML] O </ServerEntryId>
27/11/2018 15:25:34 [52758] [WBXML] O <Data>
27/11/2018 15:25:34 [52758] [WBXML] O <POOMMAIL:To>
27/11/2018 15:25:34 [52758] [WBXML] O user1@domain.de
27/11/2018 15:25:34 [52758] [WBXML] O </POOMMAIL:To>
27/11/2018 15:25:34 [52758] [WBXML] O <POOMMAIL:From>
27/11/2018 15:25:34 [52758] [WBXML] O "fbartels" <noreply@help.univention.com>
27/11/2018 15:25:34 [52758] [WBXML] O </POOMMAIL:From>
27/11/2018 15:25:34 [52758] [WBXML] O <POOMMAIL:Subject>
27/11/2018 15:25:34 [52758] [WBXML] O [Univention Help] [Apps & App Center] Mails in Outlook 2016 no longer consistent after upgrade to Kopano Core 8.6.8.2
Same email to Android-Device via ActiveSysnc:
27/11/2018 15:24:59 [52808] [DEBUG] LoopDetection->ProcessLoopDetectionTerminate()
27/11/2018 15:24:59 [52808] [ INFO] cmd='Sync' memory='1.85 MiB/4.00 MiB' time='0.25s' devType='SamsungDevice' devId='sec0760fe45db543' getUser='USER1' from='192.168.0.31' idle='0s' version='2.4.4+0-0' method='POST' httpcode='200'
27/11/2018 15:24:59 [52808] [DEBUG] -------- End
27/11/2018 15:24:59 [52755] [DEBUG] BodyPreference types: 2, 4
27/11/2018 15:24:59 [52755] [DEBUG] Remove mime body preference type because the device required no mime support. BodyPreference types: 2
27/11/2018 15:24:59 [52755] [DEBUG] GetBodyPreferenceBestMatch: 2
27/11/2018 15:24:59 [52755] [DEBUG] bpo: truncation size:'0', allornone:'0', preview:'0'
27/11/2018 15:24:59 [52755] [DEBUG] MAPIStreamWrapper::stream_open(): initialized mapistream: Resource id #122 - streamlength: 4550 - HTML-safe-truncate: true
27/11/2018 15:24:59 [52755] [WBXML] O <Perform>
27/11/2018 15:24:59 [52755] [WBXML] O <Add>
27/11/2018 15:24:59 [52755] [WBXML] O <ServerEntryId>
27/11/2018 15:24:59 [52755] [WBXML] O U8f1e2:0ee843f10bcd460cb98d440c5eed76bd86fa00000000
27/11/2018 15:24:59 [52755] [WBXML] O </ServerEntryId>
27/11/2018 15:24:59 [52755] [WBXML] O <Data>
27/11/2018 15:24:59 [52755] [WBXML] O <POOMMAIL:To>
27/11/2018 15:24:59 [52755] [WBXML] O user1@domain.de
27/11/2018 15:24:59 [52755] [WBXML] O </POOMMAIL:To>
27/11/2018 15:24:59 [52755] [WBXML] O <POOMMAIL:From>
27/11/2018 15:24:59 [52755] [WBXML] O "fbartels" <noreply@help.univention.com>
27/11/2018 15:24:59 [52755] [WBXML] O </POOMMAIL:From>
27/11/2018 15:24:59 [52755] [WBXML] O <POOMMAIL:Subject>
27/11/2018 15:24:59 [52755] [WBXML] O [Univention Help] [Apps & App Center] Mails in Outlook 2016 no longer consistent after upgrade to Kopano Core 8.6.8.2
27/11/2018 15:24:59 [52755] [WBXML] O </POOMMAIL:Subject>