Manually send delayed message
I love that Airmail has duplicated the gmail feature of delaying messages, but I've often found myself mildly annoyed by having to wait around for messages to send (unlike gmail, where the message sends immediately if you simply leave the page you sent the message from). So, I'm wondering if you could simply make a new dialog box for messages waiting to send along the lines of "Send Now." You already have a "Cancel" button on messages waiting to send; so, I would think that this would be easy to implement, and nice to have the option to manually force the email to go.
I would love this feature, too!