That's why TFA recommends buying multiple domains. He literally has a formula:

     (Desired Daily Volume / 60) x 1.1

He recommends that each domain have only 3 inboxes, and each inbox sends max 20 emails per day. So if you want to send 6000 emails per day, you should by 110 domains.

So block away! Unless you're using regexes, it won't make a big dent.

They'll eventually run out of domains.

This supposed email marketing genius has as his technique "use a bunch of VPNs to buy separate gsuite and office365 accounts, and with these accounts, send from a bunch of similar sounding domains".

I've just brought his name and business name to the attention of some people at Microsoft and Google who can get it into the right hands. I do not think this genius plan is going to work out well for him.

That would be a juicy account, they are going to get their own VIP account executive and tickets to the superbowl.

Why doesn't he just do:

  (Desired Daily Volume / 54.54)

Or even easier to remember:

  (Desired Daily Volume / 55)

Probably the same reason we write things like

SECONDS_IN_DAY = 60 * 60 * 24

The individual components have some meaning that loses clarity when we just write the result of the calculation

Alright, then. Let's assume that 1.1 is a safety factor. From whence 60?

3 sales representatives, each sending 20 cold emails per day. Yeah, it should be 3 * 20.

So if he adds more salesmen, he needs less domains? ))

I do that because I can't remember that there are 86400 seconds in day so work it out from first principles each time.

I also sing the alphabet song (in my head) when I want to know which is the 19th letter of the alphabet.