PEP8: use `except … as …` syntax in EmailServer.getMailResponse().
Fix old-style class EmailServer.MailMessage.
Remove banal truism from EmailServer.MailMessage docstring.
Remove duplicate log statement from EmailServer.replyToMail().
Fix old-style class EmailServer.MailContext.
Only log incoming emails if SAFELOGGING is disabled.
Fix old-style class EmailServer.MailDelivery.