Also, in Baker v. Libbie, the court said:
 
"From this general statement (of the rule) are to be
excepted special instances, such as letters by an agent to
or for his principal and others, where the conditions
indicate that the property, in the form or expression, is
in another than the writer."
 
    2. Where private letters in the hands of a party other 
than the writer are required for the purpose of the
administration of public justice according to the
established institutions of the country, the courts will
require them to be produced unless they would tend to
incriminate the person required by law to produce them.
This exception is well illustrated by the decision of the
Circuit Court of Appeals, Fifth Circuit, in Newfield v. Ryan
(1937) 91 fed. 2d, 700, involving two cases. In those cases
the plaintiffs sued the defendant individually and as an
employee and agent of the Securities and Exchange
Commission to enjoin the enforcement of subpoenas duces
tecum issued to the Postal and Western Union Telegraph
Companies to produce copies of telegrams sent or received
between January 1, 1937 and March 12, 1937 by the
plaintiffs or their corporations relating to Class A common
stock and certain oil leases and particularly those between
certain named persons. The District Court granted the
injunctions for the reason among others that the plaintiffs
had a property right in the privacy of their telegrams and
that the subpoenas were an attempt to deprive plaintiffs of
their property without due process of law. The Circuit
Court in reversing the decision and dismissing the suits,
recognized the property rights of a sender in his
communications but found that:
 
                        "The facts, in short, make out a
case in which the defendants, under the authority of a valid
law,
 
                                                          
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