🚀 go-pugleaf

       I used to be able to send mail (^Xm) without trouble in 18.55 - upon
       upgrading to 18.57, I find that I get an error message when I try to
       send several messages from the same emacs session.

I send large numbers of messages with C-x m in Emacs,
and never see this problem.  So I can't do anything about it.
Someone who experiences the problem will have
to figure out and tell me exactly how the failure happens.

The way to do this is to turn on the error handler: run with
debug-on-error set to non-nil.  This is the only way to understand a
Emacs lisp-level bug that gets an error; any approach that omits this
is basically hopeless.  So you can either do this yourself, or wait
and hope someone else will do it.  I suggest you do it.