Request: https://www.fec.gov/files/legal/aos/2022-14/202214R_1.pdf

Google was like "Hey, FEC, we're planning to do this thing; is it illegal? Our lawyers want to know if this counts as a campaign contribution before we start doing it and accidentally break the law". The FEC considered it and replied with a public letter stating that, in their opinion, this isn't a crime.

Final AO: https://www.fec.gov/files/legal/aos/2022-14/2022-14.pdf

Any other email provider could do the same now of course: it's just an opinion about the law, not a rule specific to Google.

Google also could have gone ahead and just done it, of course, but having the AO in hand puts the lawyers at ease.