Although as fundraisers, we like to engage with our supporters from the start, we can often benefit from using marketing lists obtained from third parties.
These seem to be used less for electronic mail marketing these days, due to the sensitivities around evidencing consent, but are still popular for postal direct marketing.
And of course, you may often receive personal data from third-party fundraising platforms and the like.
The ICO has revamped it guidance on using marketing lists and it is well worth reviewing, to check that you can demonstrate compliance.