Exchange 2013/O365 hybrid setup.
2 domains, AADConnect
A Shared mailbox on O365, synced from an AD user of 2nd domain, is getting lots on NDRs of the IMCEAX type.
Adding the IMCEAX as proxyaddress to the destination mailbox allows emails to be sent.
Problem is, I have a large user base (> 100.000 users) and just the tracking logs to examone to solve this issue. Tracking logs do not show, as far as i know, the smtp sender but just the undecifrable missinng encapsulated SMTP (i.e. the IMCEAX address which corresponds to the missing legacyExchangeDN value)
So I would like to
- be albe to understand why out of a sudden these addresses generate NDRs (no changes have been done on users as far as i know)
- be able to match the IMCEAX NDR to a corresponding smtp address
- is it correct all mailcontacs on prem (for these users) have a legacyExchangeDN empty? I believe not.