Just wanted to let members know that when you create a post in a topic it appears immediately on the web interface, but Discourse intentionally delays the sending of the email by a configurable time, default ten minutes, so that you can go back in and edit and correct before the mail item goes out to the group. This is because one invariably finds mistakes after one has posted!
Typical outbound send times are therefore of the order of ten minutes, no longer, and no shorter. A question was asked of me how long to expect to see mail, hence this post. None of this applies to digest forms, which follow completely different timing parameters and criteria.
With regard to replies initiated from your own mail program, they come through into the topic and are displayed immediately on receipt.