why should I add a domain name?

[khalid]

Hello,

I'm ex-GR PRO user!

I used the PRO account for 1 year. I want to re-new now.
but I'm a little bit worried about deliverability issues.

here is my question:

as I want to ensure the best deliverability and response from
my subscribers, I will do what GR recommends as using double
opt-in and adding a domain name.

now I know why switching to double opt-in is good, but, why
using a domain will increase my deliverability? what's the point?

is it to have unique IP?


Thanks in advance,
Kaled.