[teddyh]

From what I understand, this is incorrect:

> SPF and DKIM are used as indicators of whether an email is spoofed or not. But if you added an SPF record on your domain, and you forget to add one of your email systems - say, Postmark, which you use to send mission-critical notifications from your application to your customers - then your customers could stop getting emails. If you added DKIM keys to your domain, but one of your email services doesn't support DKIM - or you forgot to add DKIM keys for that service - your customers could stop getting emails.

Setting up DKIM alone for one email service should still allow mails sent by any other email service (i.e. one not using DKIM) to be delivered. (That is, of course, if DMARC is not also set up with a strict policy.)

That is to say, DKIM is not that risky to set up and use, by itself.