While creating a Distribution Group, you set the owner / manager of the group. The owner has permission to add and remove members from the group, process requests to join and moderate messages if configured to do so. If you have given ownership to an individual, but haven't added your own account, you won't have permission to change the Distribution Group settings. To add additional group owners, you will need to use PowerShell and bypass the Security Group Manager check.
Install the Windows Azure Active Directory (WAAD) Module - http://technet.microsoft.com/en-us/library/jj151815.aspx#bkmk_installmodule
Connect WAAD PowerShell to Exchange Online
$LiveCred = Get-Credential $Session = New-PSSession -ConfigurationName Microsoft.Exchange -ConnectionUri https://ps.outlook.com/powershell/ -Credential $LiveCred -Authentication Basic -AllowRedirection Import-PSSession $Session
Example 1 - adds a new group owner/manager.
Set-DistributionGroup -Identity ["Distribution Group"] -ManagedBy [manager] -BypassSecurityGroupManagerCheck
Example 2 - Adds two new group owners to all distribution groups
**Take care when using this command. It replaces the existing group owners/managers with the users you list in the command.
Get-DistributionGroup | Set-DistributionGroup -ManagedBy [manager1], [manager2]-BypassSecurityGroupManagerCheck
The ManagedBy parameter specifies the name of the mailbox recipient that appears on the Managed by tab of the Active Directory object. If this parameter isn't specified, the creator of the group is the owner.
This parameter accepts the following values:
- Alias Example: JPhillips
- Display Name Example: Jeff Phillips
- SMTP Address Example: Jeff.Phillips@contoso.com
- User Principal Name Example: JPhillips@contoso.com
The recipients specified with the ManagedBy parameter aren't automatically members of the distribution group. If you want recipients specified in this parameter to be added as members of the distribution group, you need to add them as members.
The Set-DistributionGroup command http://technet.microsoft.com/en-us/library/bb124955(v=exchg.150).aspx