Why is Yahoo Mail being discriminated?

[Corzhens]

I wonder why Yahoo is being discriminated by some sites. When I joined a social media site that pays the members for their posts, I was surprised to receive an error message upon registration. That the site accepts only Gmail and my Yahoo email is not valid. This morning I tried to sign up with a site for freelancers. There was a portion in the form that asks for the working email. I indicated my Yahoo email and another message said that I might want to indicate my working email as if my Yahoo email is not valid. I wonder why there is discrimination of Yahoo Mail going on. Any ideas?

[Henrywrites]

I don't really think that there is need for some ofthose sites to reject a working Yahoo mail account. The reason is because as the member, you are always ready to receive some mails and I don't think that has got to be an issue with those people that are handling those sites.