[LeonM]

For DMARC alignment you need either SPF alignment or DKIM alignment, either one will do. (note that 'alignment' is not the same as an SPF pass).

Which means that you _could_ get away with just SPF alignment, but you wouldn't want to trust on that since SPF is horribly broken and most third party senders don't even bother with SPF alignment anymore. Always focus on DKIM alignment instead.

But if you are now just thinking about this, you're in trouble anyway. If you are sending bulk amounts of email (that is, 5k a day per Google's rules) and you are not yet signing with DKIM, then you are probably not ready for adopting a strong DMARC policy ('quarantine' or 'reject') before Feb 1st.

Email hardening takes time, the larger/more complex your domain is, the more time you probably need to ensure you are DKIM aligned for all your delegated senders. Don't be tempted to just add a DMARC record with p=reject policy, that would be irresponsible and asking for problems (read: undeliverable email).