Hi @William Fahham ,
If you are an On-Premise user, you could apply a retention policy using distribution groups by running the command below in EMS:
Get-DistributionGroupMember "<GROUP NAME>" -ResultSize Unlimited | Get-Mailbox | Set-Mailbox -RetentionPolicy "<POLICY NAME>"
If you are an O365 user, you could use the existed options to Include or Exclude the security or distribution groups you would like, just like below:
Hope these could help.
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