A quick workaround should be to extract the quoted field separately from the _raw data. You can do it through field extractions or props.conf and transforms.conf. Here I would give you the example using inline rex command:
-- Your query -- | eval _raw = " 2016-12-20T14:33:54.693Z,fe80::b9c4:56fa:d460:81f3,exchangesrv.test.com,fe80::b9c4:56fa:d460:81f3%12,exchangesrv,\"MDB:bdfe3301-0f8f-48ce-92e4-6ff938ad1a6d, Mailbox:6a2dac65-cadc-46ec-b44c-98fba096c55e, Event:156022, MessageClass:IPM.Note.ProbeMessage.MBTSubmissionServiceHeartbeatProbe, CreationTime:2016-12-20T14:33:54.599Z, ClientType:Monitoring, ServerMdbConnectionId:08D423660D5DE7FD\",,STOREDRIVER,RECEIVE,2014,,4c7b2b2e-291a-4635-f603-08d428e539b5,
[email protected],To,8944,1,,,0000003a-0000-0000-0000-0000f519e953-MBTSubmissionServiceHeartbeatProbe,
[email protected],
[email protected],04I: ,Originating,,,,S:MailboxDatabaseGuid=bdfe3301-0f8f-48ce-92e4-6ff938ad1a6d;S:ItemEntryId=00-00-00-00-2D-E8-87-0C-DF-D8-A0-42-97-64-3D-D7-57-8C-2A-3C-07-00-E7-FB-62-04-97-51-5F-44-B6-C5-9B-A3-65-97-9D-5F-00-00-00-00-01-0B-00-00-E7-FB-62-04-97-51-5F-44-B6-C5-9B-A3-65-97-9D-5F-00-00-1E-84-2C-F6-00-00;S:DeliveryPriority=Normal;S:AccountForest=test.com;S:IsProbe=true;S:PersistProbeTrace=False,Email,940aee54-2531-41e4-f603-08d428e539b5,15.01.0544.027" | rex field=_raw "\"(?<quoted>.*)\"" | table _raw quoted
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