This is off-topic, but since a fair number of web2py users send e-mail from their applications, I thought this post from 37Signals might prove helpful to some.
There were nearly 16 million e-mails sent from 37Signals' eight web applications in the last seven days. About 99.3% of them were accepted by the remote mail server. The link explains how they achieve such a high rate of acceptance. http://37signals.com/svn/posts/3096-behind-the-scenes-giving-away-the-secrets-of-email-delivery
