Installing DKIM and SPF records
You only need to do this if you have your own domain. e.g. xrnottingham.org
Setting this up helps improve the delivery rates to inboxes (rather than going to jumk/spam).
The extinctionrebellion.uk domain has already been set up. So if you use an email address as your reply-to email, then you don't need to do anything.
More info on @extintionrebellion email addresses here.
It is not possible to set up DKIM/SPF for gmail/hotmail/aol/outlook etc. These should already be recognised domains.