SPF records were centrally added to all top-level domains (unit.ox.ac.uk) in 2016. This was a one-off exercise, and we recommend that local ITSS add the default SPF record to any domains they use in email sender addresses.
Some background on why we introduced SPF records, and their impact in relation to some ISP mail providers and common scenarios is available in the ITSS wiki.
Please do ensure that you understand SPF before amending records, as even a syntactically correct entry can render your entire SPF invalid. Consult a suitable SPF guide or the associated RFC for details.