finding which provider is responsible for the mail domain

By provider, I mean the provider responsible for mail, e.g. for gmail the provider would be gmail(or/by google) and for microsoft.com it would be outlook(by microsoft).

Basically, I want to find out given an email domain e.g. abc@xyz.com, hxy@tuv.com is from a specific provider(outlook or gmail) in our case, since xyz or tuv is not explicitly evident which provider it belongs to.

I have succeded somewhat, my idea being to make use of MX records, so I do something like this in nodejs:

const dnsMod = require('dns');

dnsMod.resolveMx(
    'mydomain.com', (err, value)=>{
        console.log('The error is : ', err);
        console.log('The value is : ', value);
    }
)  

and it returns records like this:

[
  { exchange: 'alt3.gmail-smtp-in.l.google.com', priority: 30 },
  { exchange: 'alt1.gmail-smtp-in.l.google.com', priority: 10 },
  { exchange: 'gmail-smtp-in.l.google.com', priority: 5 },
  { exchange: 'alt2.gmail-smtp-in.l.google.com', priority: 20 },
  { exchange: 'alt4.gmail-smtp-in.l.google.com', priority: 40 }
]   

so, seeing this we can conclude the provider in this case is infact gmail.

But, my point is, is it safe to conclude the provider is gmail just it contains words like google, gmail etc. In other words, do google's mail servers always have a google.com in the end, (or Similarly, microsoft's mail provider have outlook.com or microsoft.com in the end)? If not, what better way would be to confirm this?

EDIT: As per suggested by comment, I need the information because, based on the information I need to show only one of google or outlook button.