unlisted-recipients:; (no To-header on input)

[kvalo]

In an accepted email the Cc header contains:

Cc: unlisted-recipients:; (no To-header on input)

https://lkml.kernel.org/r/20191001111912.A75D36014B@smtp.codeaurora.org

Though rest of the Cc and To field looks ok.

[kvalo]

The problem comes that the original patch didn't have To field either:

To: unlisted-recipients:; (no To-header on input)

https://lkml.kernel.org/r/20190926225604.9342-1-efremov@linux.com

So pwcli should not copy that without checking that the email address is valid.