Was there ever a time where 'enclosure' was used as an alternative to 'attachments' of an e-mail?

Question

In a recent interview, Bill Gates used the word 'enclosure' instead of 'attachment' while referring to e-mail attachments. Both of those words have been used interchangeably when referring to traditional media and mail (even though they differ in meaning), but I have never heard anyone use this word with respect to digital mail.

While researching for this question, I found this ELL Post which also seemed to agree that the word enclosure has never seen much use in terminology associated with digital mail.

Was there ever a time where 'enclosure' was used to refer to media/documents in digital mail?

Answer 1

FEMA Instruction 5400.4 of 15 March 2000 has

4. Documentation Requirements for E-Mail Messages That Are Records. Hard copy printouts of E-mail records must include all pertinent identifiers that make the message intelligible.

   ...

   b. Additional Requirements. When necessary for complete documentation, print out:

   1. Enclosures. Print out enclosures only once if the same enclosure is being sent to multiple addresses.

So the term was in use in the US Federal Government in 2000. That document supersedes Temporary Directive 96-01(T), Electronic Mail Recordkeeping Guidance dated 27 March 1996, and it's possible that the term appears that early. However the earlier document does not appear to be available online to check.