Email script not sending as @gmail or @hotmail

[fake01]

I have an email script which is currently working. But it took several hours to figure out the problem. When I put the senders (me) email address as @gmail or @hotmail extension, it refuses to send the email. But if I have the extension as @example or @test (haven't tried any others) it works and sends the email perfectly fine.

Now there is nothing in my script which is filtering out those extensions. And my script obviously works. SO I am wondering if the server is filtering out those extensions somehow? and if so is there a way to allow those extensions through?

Doesn't work:

$from = "From: ".EMAIL_FROM_NAME." <mathew.odonoghue@gmail.com>";

$from = "From: ".EMAIL_FROM_NAME." <mathew.odonoghue@hotmail.com>";

Works:

$from = "From: ".EMAIL_FROM_NAME." <mathew.odonoghue@lol.com>";

$from = "From: ".EMAIL_FROM_NAME." <mathew.odonoghue@example.com>";

$from = "From: ".EMAIL_FROM_NAME." <mathew.odonoghue@test.com>";

 

[descalzo]

Seems to be an ongoing problem.
I am not sure if the mail server is set up that way to prevent spam/phishing or what.
The Admins have yet to address this issue as far as I can recall.