As a Microsoft Exchange Administrator, Bad Items in mailbox migrations have always been a pain. It is upsetting to see a large number of bad items in migrations because no one likes the idea of data loss.
As outlined in the document called “Track and Prevent Data Loss”, in January 2020, Microsoft rolled out an improvement to the process of handling Bad Items in MRS moves. This was done through a new process called Data Consistency Scoring. (Read the detailed documentation here: https://docs.microsoft.com/en-us/exchange/mailbox-migration/track-prevent-data-loss-dcs).
In summary, this process grades migrations and basically gives classification to the types of bad items. Thus we can ignore the known types that are of little concern. Simply put. . . we can now focus on real MRS errors instead of the time-consuming stuff that we can typically ignore.
In the past versions of Exchange, we did in fact see some corruption in server storage. With the advances in storage and improvements over the years, this kind of corruption just isn’t common anymore. These days, the most common issues are corruption caused from bad imports, sometimes done a while ago. These include:
- Poor imports from an OLM / OLM Conversion or other formats
- Poor PST imports or other external data
- Bad metadata – mainly Mailbox Permissions
Bad Data Imports
As someone who works in the Migration space, I know the importance of following the rules and confirming that our technology works correctly. However, this isn’t always the case. Sometimes people use inexpensive tools and they cut some corners. Perhaps the best examples of this are processes that poorly convert other mail formats and then import them into the Mailbox. From my experience, the worst offenders are processes that have converted OLM files or other Apple storage options. It just seems time and time again, poor conversions and imports are done. At the time they seem fine, but during these migrations the MRS process finds items, often not viewable to the users, that were not converted or imported correctly.
Bad Meta Data
Hands down the most common Bad Items are old and invalid mailbox permissions. These permissions will not come over when moving to Office 365 and they have been flagged as Bad Items. As an admin, I really don’t have a great way to fix these and just need to ignore them. To me, this is the largest improvement made with this new Data Consistency Scoring.
The lesson? Stop using the old method and embrace the new Data Consistency Score! Need some extra help on how to do this? I’ve done a great overview on the Practical 365 BLOG and that article can be read here: https://practical365.com/exchange-online/data-consistency-scoring-for-exchange-online-mailbox-migrations/
