Email sent via Sendgrid getting late delivered to customers - laravel-4

Question

We are using SendGrid to send email to customers once they get registered on our website.
We have two portals:
One is live, and another is a test portal.
When customers are signing up in the live portal, the email is getting delayed about 5 minutes to reach the customer, but when the customer is receiving the mail after 5 minutes, the time of receiving mail is showing exactly the same time at which customer did signup.
Whereas in the test portal, emails are getting delivered at the correct time.
The code in both portals are totally the same.
This problem is happening with only Gmail, but I am not able to find out why emails are getting delivered late in live portal.
If anyone faced this same problem before, can you please guide me to solve this?
Here below is the code to send email
if($input['email']!= ''){
$email = $input['email'];
$username = Input::get('name');
$password = Input::get('password');
if($userdata->email != '')
{
Mail::send('emails.templates.activation',
array('username' => $username,'customer'=>$customer,'code'=>$code), function($message) use ($userdata) {
$message->from('support#buynuse.net', 'Buynuse');
$message->to($userdata->email, $userdata->username)->subject('Please activate your new Buynuse account');
});
}
echo 'email';exit;
}