We have a few users who received the spam notification message from EOP, and clicked on the "Release to inbox" while also having the sender in their blocked senders list.

So, EOP happily sent the messages to our internal Exchange servers, where our Hub Transport Servers block the messages due to Sender Filter Agent.

My question is:

Is there any way for an administrator to re-release these, or does the user need to contact the sender and ask the sender to resend?

EOP's PowerShell documentation on Release-QuarantineMessage seems to indicate that I can release to an administrator via the User parameter:

The User parameter specifies the email address of the user to whom you want to release the quarantined message. You can specify multiple email addresses separated by commas.

The message is released only to the recipients specified by this parameter. If you want the message released to recipients who are also administrators, be sure to include them in the list.

If you previously used the ReleaseToAll switch to release the quarantined message to all original recipients, and you later release the message again with the User parameter, any original recipients you specify with the User parameter are skipped.

However, when I attempt that, I am told that the message cannot be released.