Export DL Memberships from Exchange 2013 and Import to 365 via PowerShell

Hello Curious_Kevin16,

Script provided by elieelkarkafi is for exporting data from M365 and will not fit directly to your use case.

In your case logic is pretty straight forward:
Exchange Server
1. Get All Distribution Lists
2. For each group  export Members

M365
1. For each Exchange server DL get exported members
2. Foreach member add him/her to DL in M365

Example code:

#Exchange Server
$DistributionList=Get-DistributionGroup
foreach($dl in $DistributionList){
 Get-DistributionGroupMember -Identity $dl.Name | Export-CSV -Path "C:\Temp\$($dl.Name)-DLMembers.csv"
}

#M365
#Connect to Exchange Online
$DistributionList=Get-ChildItem -Path "C:\Temp" -Filter "*-DLMembers.csv"
foreach($dl in $DistributionList){
 $Memberships = Import-Csv -Path $($dl.Name)-DLMembers.csv"
 foreach($m in $Membership){
  Add-DistributionGroupMember -Identity $dl.Name -Member $m.PrimarySmtpAddress
 }
}

Please note that this sample code will not handle expanding group which is a member of another group.

Hope that helps.