Using Alternative Data Research (Providers for sourcing hedge funds) tracking Sendgrid growth. When generating a new SPF record in Sendgrid's admin panel I suspect one entry in particular is the underlying User ID (sequential) of the account.
By periodically digging new domains and looking for Sendgrid's TXT records it's possible to estimate their new customer join rate.
And it looks to be the case. A uid from an account registered on 5/21/2018 is 7,622,464. Another from 5/26/2018 is 7,654,903. So current new account join rate is ~6,500/day.
To track active customer growth over time would be a much larger project but easy enough. I would setup a massive dig scraper running it against all .com and .net zone files and see the change in sendgrid's dns presence. Since one would be performing hundreds of millions queries just for one run, I'd probably schedule it on a monthly basis.
Alternatively, one can just create new accounts periodically and create the SPF records directly.
View historical DNS TXT Records at Historical DNS TXT Records | Rook Research
