net/smtp: adds support for the SMTPUTF8 extension
If the SMTP server supports the SMTPUTF8 extension,
the SMTPUTF8 parameter is added to the MAIL FROM
command by the (*Client).Mail method.
Fixes #19860
Change-Id: I3287faf114ee514e5faa815a6bbc1bf04cf60b0f
GitHub-Last-Rev:
d6338bb802da7537223f1ec6eda960606febefb8
GitHub-Pull-Request: golang/go#40627
Reviewed-on: https://go-review.googlesource.com/c/go/+/247257
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>