Hi Divya,

check if they are receiving mail in Junk box or spam folder. because some security reason mail goes to spam.

Regards

RS 

Hi Divya,

If mails are received on some domains, but not by others, most likely it's a spam detection issue, like Rahul already said. This can be caused because you send the mail through an untrusted or even blacklisted provider, or because your e-mail contains elements typically found in spam mail, like tracking pixels, an abundance of links, etc.