Using a Stock Photo for E-mail Marketing

Not an expert myself, but I can corroborate what Abambo is saying. Not using the work in a way that people can extract it: that refers to the original, full resolution image. For example, if you were bundling a bunch of images to provide as assets for another designer, you can't purchase rights to an Adobe image and add it to your bundle. You have a right to use the original you downloaded, but you can't just give it to someone else for the same purpose.

Using it in a layout for email marketing purposes is not the same, so you should be fine!

Exactly, there is no way to stop a third party to extract the work. But you will not insert the full-size work, but a heavily reduced and optimized asset.

I think you can easily use Stock images for marketing purposes, also via e-mail marketing. I even think that e-mail marketing is somewhere noticed on the licencing pages.

Look here for more information on licensing: https://community.adobe.com/t5/stock/links-for-licensing-terms/td-p/11366788
(Disclaimer: As always with licensing, this is my interpretation of the rules. I think they are correct and advice is based on reading and interpreting the licence terms and on fair use for both the buyer and the artist/stock company, but I cannot rule out that my interpretation is wrong. I'm not an Adobe employee).