Hi all,
I have a simple email sender for user account activation. Depending on which email address I use, I get significantly different response times: University email - 1 minute, Gmail - 3-4 hours, Yahoo - 1 or 2 days -- which seems bizarre. Has anyone else seen this phenomenon?

EDIT:

There weren't many responses (even for a bounty), but I'll try to explain my problem more clearly.

This probably isn't greylsting -- If I so a simple:

php mail ($to, $subject, $body) // this delivers instantly.

My cakephp code:

    function __sendActivationEmail($id) {
    $User = $this->User->read ( null, $id );
    $this->set ( 'suffix_url', $User ['User'] ['id'] . '/' . $this->User->getActivationHash () );
    $this->set ( 'username', $User ['User'] ['username'] );
    $this->Email->to = $User ['User'] ['email'];
    $this->Email->subject = 'Test.com - ' . __ ( 'please confirm your email address', true );
    $this->Email->from = '[email protected]';
    $this->Email->template = 'user_confirm';
    $this->Email->sendAs = 'text';
    $this->Email->delivery = 'mail';
    $this->Email->send ();
}

Causes delays from 13 minutes (ok; we'll deal with it) to 5-6 hours (less okay, since this is an activation email). For some of my users, it works instantly, but for other users (of the same service provider, i.e., gmail, it sees these delays).

Any clues?