Add multiple members to a distribution group in O365

To create bulk distribution groups at one time, and add multiple members to each distribution group, please take to the following steps:
1. Install and configure Windows PowerShell.
2. Connect Windows PowerShell to Exchange Online.
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Create bulk distribution groups at one time
1. Prepare a CSV file to import multiple distribution groups, and store it in local disk (for example, C:\distributiongroups.csv ).

For example:
Name, Type
Group1, Distribution
Group2, Distribution

Note:
Name represents display name of the distribution group.

2. Run the command below to bulk import several distribution groups:
Import-CSV “D:\distributiongroup.csv” | foreach {New-DistributionGroup -Name $_.name -Type $_.Type}

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Add multiple members to each distribution group
1.Prepare a CSV file to contain each user’s information, including Display name, Alias, E-mail address, and then store it in local disk (for example, D:\list.csv ).

For example:
Display name, Alias, E-mail address
Member1, member1, member1@contoso.com
Member2, member2, member2@contoso.com

2. Import the CSV file to Exchange Online via PowerShell.
Run the cmdlet:
Import-Csv “D:\list.csv” | foreach{Add-DistributionGroupMember -Identity “GroupName” -Member $_.alias}

Note:
GroupName represents the distribution group needs to be added members.
After those steps, you can create multiple distribution groups at one time, and add several users into them.