Can't send mail with smtpmail "any more". (Gmail and other providers)

[Vladimir Nikishkin]

Hello, everyone.

I had a setup for sending mail with Emacs' smtpmail:

```
(setq send-mail-function 'smtpmail-send-it)
(setq smtpmail-smtp-server "smtp.gmail.com")
(setq smtpmail-default-smtp-server "smtp.gmail.com")
(setq smtpmail-smtp-service 587)
(setq smtpmail-stream-type 'starttls)
(setq smtpmail-starttls-credentials '("smtp.gmail.com" 587))
(setq smtpmail-smtp-user "lockywolf")
(setq smtpmail-auth-credentials '("smtp.gmail.com" 587))
(require 'starttls)
(setq starttls-use-gnutls t)
(setq smtpmail-debug-info t)
(setq smtpmail-debug-verb t)
(require 'smtpmail)
```

This used to work until today.

Today, this setup stopped working for some reason. Initially I blamed
it on GMail, but it seems that other providers don't work tool.

The symptom is the following:

-- 
Yours sincerely, Vladimir Nikishkin
(Sent from GMail web interface.)