Add Bulk Users in Distribution Group

Please refer to the instructions and the cmdlet tested in our test environment with details below to successfully add bulk users to a distribution group.

1. Create a DL (if not already)

Note: We created a DL with name = 15432-DL and email address = [e-mail]

2. Prepare a CSV file to contain each user’s information, with parameters Display name, Alias, E-mail address, and then store it in local disk 

Note: We created a CSV file using the following parameters
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3. Connect to Exchange Online PowerShell.

4. Import the CSV file to Exchange Online via PowerShell using the cmdlet below,

Import-Csv “C:\filename.csv” | foreach{Add-DistributionGroupMember -Identity “GroupName” -Member $_.alias}

Note: We used the cmdlet Import-CSV C:\Test2-15432.csv | ForEach {Add-DistributionGroupMember -Identity "[e-mail]" -Member $_.alias}

4. Were able to add the members to the DL successfully

Note: You can refer to Add bulk users in distribution group - Microsoft Community as well