1. Name your email server with "mail" some where in the name. Seriously don't call your email server crapbox.snaphop.com :)
2. Although you can send email as a relay on many different ports (2525, 8025, 587 (ssl)) you can really only receive on port 25.
3. You better have a PTR / reverse dns setup.
4. It takes at least a couple of hours before email servers will acknowledge you.
5. You can get away with out a SPF for a little bit but you really need if your going to blast a crap load of emails. Use this to test: http://www.kitterman.com/spf/validate.html
not sending that much mail, but noticed after setting up SPF/DKIM/reverse DNS that the mail I sent to myself didn't end up in spam folders at gmail and hotmail etc., without having to send via a service like authsmtp.com.
If you can live with delayed messages there is not really a need for fail-over as most server will retry multiple times (default iirc multiple days). But you should have at least another email address available for example to communicate with your provider.
Some things that are rather important:
1. Name your email server with "mail" some where in the name. Seriously don't call your email server crapbox.snaphop.com :)
2. Although you can send email as a relay on many different ports (2525, 8025, 587 (ssl)) you can really only receive on port 25.
3. You better have a PTR / reverse dns setup.
4. It takes at least a couple of hours before email servers will acknowledge you.
5. You can get away with out a SPF for a little bit but you really need if your going to blast a crap load of emails. Use this to test: http://www.kitterman.com/spf/validate.html