Ediscovery Search Limits

Hi Everyone,

I have to run an eDiscovery Search across all 100k+ mailboxes with messages from a specific sender/ author AND with a specific Subject.

The issues is we have A3 licensing and we are limited to 10k mailboxes per search.

I have tried creating groups and importing a list of 10k users via CSV but my Powershell sessions either take FOREVER or times out.

Import-Csv -Path C:\StuGrp1.csv | foreach{Add-DistributionGroupMember -Identity StudentGroup1 -Member $_.Mail}

What other options to I have to run this type of search and bypass these limits?  From what I am given I don't really have any options to limit my scope by anything else.

I also tired to search one month at a time but that still searches across 100k+ mailboxes.

Thanks for any help!

Ian...