alt Hacker NewsUsing both has to be done very carefully, because a positive result from the weaker one (SPF) will override a negative result from the stronger one (DKIM). You should maximally use DKIM and minimally use SPF. Ideally, you should not use SPF at all, but there are some senders that still don't support DKIM.
Replies
daneel_w • yesterday at 7:27 PM
The "logical OR" of DMARC is absolutely a glaring caveat. I run my own MX and would personally under no circumstance omit SPF, because I consider neither SPF nor DKIM complicated enough to warrant consideration.
Many email providers and third party security tools default settings automatically bounce or block SPF failures, no matter what DKIM says... so no, not using SPF completely is a bad idea.
Using it minimally is correct, thou. Route outbound mail through as few controlled relays as possible so your SPF record only needs to list infrastructure you actually *own*, rather than growing it every time a new tool needs to send mail.
I have seen way too many clients almost hit the char limit in a TXT record