In Microsoft Office 365 dedicated/ITAR, Full Access and Send As permissions for security groups that an administrator added by using Exchange Admin Center (EAC) to Microsoft Exchange Server 2013 mailboxes can’t give group members the correct access. Administrators will see that the managed group object is listed as having permissions. However, members can’t access the mailbox or send as the mailbox.
Note Full Access and Send As permissions for user objects that were added by using EAC will work as expected.
To work around this issue, administrators who are members of the SSA-Mail Recipients (MR) role group should grant permissions to groups by using Remote PowerShell.
Note You should always specify the source user or group object in the User parameter when you use Remote PowerShell in the format Domain\samAccountName. You shouldn’t specify the SMTP address or alias, because this will add the managed object to the permission list.