HELO Header missing

Hi, that is not a problem with the plugin, is the receiving server refusing emails from your server, you should check with your provider, especially if that error happens with all emails. In this latter case, the problem can be in the mailing service of your hosting provider.

Well, it *is* a problem with the plugin, as long as you do not emphasize that a separate SMTP plugin is definitely needed to meet all the antispam regulations of email providers.
In fact, there are plugins around that include a HELO/EHLO command by default (which is not very difficult). I thought you were able to do so, too.
Anyway, I downloaded one of the SMTP plugins around, and I hope this will work.

Hi, the HELO command is sent by your mailing service, not by the plugin. Every plugin and WP itself uses the wp_mail() function that, in turn, uses the PHP mailer library included in WP that uses the mail() function of PHP. The mail() function uses the sendmail command or, on Windows, PHP can be configured to talk directly with an SMTP server. A plugin can use directly the PHP Mailer library (or other libraries) to connect directly to an SMTP server. Newsletter has a free addon to deliver via SMTP, but a specific SMTP plugin can offer more features.

As far as I know, no plugins implement the full SMTP protocol stack, a library is typically used. But if you know of plugins implementing the HELO command, and so the SMTP protocol, I’m interested in checking them.

Thank you.