WordPress.org

This plugin replaces WordPress' internal email sending functionality by routing all email through Postmark, greatly enhancing email reliability. If you rely on your WordPress install to send you email, this plugin along with the awesome service from Postmark makes sure that it actually does reach its destination.

Why you should use this plugin over the official Postmark approved plugin or other Postmark plugins?

• Uses the WordPress HTTP API instead of CURL, so it even works when there's no CURL available.
• This plugin sends your email over a secure (SSL) connection (and actually checks whether the host on the other side is really the host we expect).
• Handles From / CC / BCC headers correctly, when set by plugins like Gravity Forms.
• The plugin handles attachments correctly.

More info about the plugin:

• Sending reliable email with Postmark.
• Plugin page on yoast.com.