I said that "this is a basic HELO tool (or EHLO now), it is very popular with spammers, lead-gens and prospectors and WILL definitely harm the deliverability if the IP address making the call.
If you are thinking that you need one, you’ve probably collected your data badly.
If you decide to make one to test large numbers quickly, whatever you do, don’t use the same IP address that you want to send emails or host images and webpages on"
If you need to check your addresses, I doubt you have permission to email them in the first place or you have not emailed them in a long time. Either way, if you think you could use it, you need to look at how you email first.