PHPMailer enables SMTPAutoTLS by default, meaning it opportunistically
upgrades a plain SMTP connection to STARTTLS whenever the server
advertises support for it, regardless of the 'secure' => '' setting
documented in config.default.php. Minz_Mailer never read or set
$mail->SMTPAutoTLS, so this behaviour could not be turned off, making
it impossible to talk to SMTP servers with a self-signed or otherwise
untrusted certificate (e.g. a mail server on an internal Docker
network) without importing a custom CA.
Add a new 'auto_tls' key to the 'smtp' config array, defaulting to
true to preserve current behaviour, and wire it through to
$mail->SMTPAutoTLS in Minz_Mailer. Document the new option.
Fixes#2997
Co-authored-by: Gerard Alvear <gerard.alvear@logiqd.me>
5f94330503