He guys, I would like to see support for using postmarkapp.com as a sender. It is possible with the SMTP method today, however they require a special header to be used to send to a specific "stream". Example:
X-PM-Message-Stream: broadcast
They also support sending metadata, and tags in the headers, so supporting this would be great. If there is any documentation on how to do this now via hooks/filters that would be great.