IMCEAEX non-delivery report


When migrating from on-prem Exchange to Office 365, it's best to treat it like any other cross-forest move and populate each object's LegacyExchangeDN value as an X500 address, otherwise you'll get NDR errors replying to old messages or calendar entries once mailboxes start moving.

When receiving IMCEAEX NDRs, you can use the contents of the error to determine the missing X500 and then add it back to the proxyaddresses array for the object and let that sync to O365.

 

Example :

IMCEAEX-_O=ForestA_OU=EXCHANGE+20ADMINISTRATIVE+20GROUP+20+28FHSDHJF23GHYED+29_CN=RECIPIENTS_CN=John+2ESmith@namprd01.prod.outlook.com

Resolution :

Remove IMCEAEX- and replace with x500:

x500:_O=ForestA_OU=EXCHANGE+20ADMINISTRATIVE+20GROUP+20+28FHSDHJF23GHYED+29_CN=RECIPIENTS_CN=John+2ESmith@namprd01.prod.outlook.com

Drop the @xxxxx from the end

x500:_O=ForestA_OU=EXCHANGE+20ADMINISTRATIVE+20GROUP+20+28FHSDHJF23GHYED+29_CN=RECIPIENTS_CN=John+2ESmith

Replace _ with /

x500:/O=ForestA/OU=EXCHANGE+20ADMINISTRATIVE+20GROUP+20+28FHSDHJF23GHYED+29/CN=RECIPIENTS/CN=John+2ESmith

Replace +20 with spaces

x500:/O=ForestA/OU=EXCHANGE ADMINISTRATIVE GROUP +28FHSDHJF23GHYED+29/CN=RECIPIENTS/CN=John+2ESmith

Replace +28 with (

x500:/O=ForestA/OU=EXCHANGE ADMINISTRATIVE GROUP (FHSDHJF23GHYED+29/CN=RECIPIENTS/CN=John+2ESmith

Replace +29 with )

x500:/O=ForestA/OU=EXCHANGE ADMINISTRATIVE GROUP (FHSDHJF23GHYED)/CN=RECIPIENTS/CN=John+2ESmith

Replace +2E with a period (.)

x500:/O=ForestA/OU=EXCHANGE ADMINISTRATIVE GROUP (FHSDHJF23GHYED)/CN=RECIPIENTS/CN=John.Smith

 

Just take this value and add it to the proxyaddresses array of the user in Exchange Onprem, sync to O365 and bam!

 

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