What percentage of email servers do you think are configured wrong as
pertains to RFC2821, Seems like a lot of people have their servers
set to automatically return a permanent failure message when smtp is
temporarily down. Sending Strategy

The general model for an SMTP client is one or more processes that
periodically attempt to transmit outgoing mail. In a typical system,
the program that composes a message has some method for requesting
immediate attention for a new piece of outgoing mail, while mail that
cannot be transmitted immediately MUST be queued and periodically
retried by the sender. A mail queue entry will include not only the
message itself but also the envelope information.

The sender MUST delay retrying a particular destination after one
attempt has failed. In general, the retry interval SHOULD be at
least 30 minutes; however, more sophisticated and variable strategies
will be beneficial when the SMTP client can determine the reason for

Retries continue until the message is transmitted or the sender gives
up; the give-up time generally needs to be at least 4-5 days. The
parameters to the retry algorithm MUST be configurable.