In Chief Counsel Email 201545025 the issue involved whether the use of an approved private delivery service was acceptable for delivery to the IRS of notices of non-judicial sales.

IRC §7425 deals with the IRS’s rights when the service obtains a lien on property.  Generally such a lien is not impacted by any judicial proceeding to which the IRS is not a party.  A limited exception occurs in certain cases described in IRC §7425(b) if the IRS is properly notified of the proceeding.