For some transactions : CGI2 not ok

Hello,

I use OC 2.0.1.0 and CM-CIC payment module.
I have tested the module on about 30-40 transactions.
Most of the time, it works well, ut in some cases i get "CGI2 not ok" with the following warning :
<b>Notice</b>: Error: DATA not accepted from server! in <b>/home/operap6/public_html/system/modification/system/library/mail.php</b> on line <b>424</b>

When I look into the mail.php around line 424 I find the code :
if (substr($reply, 0, 3) != 250) {
trigger_error('Error: DATA not accepted from server!');
exit();
}

In those cases :
- the order is successful in my system (order is added)
- my payment gateway indicates a successful payment
- the order confirmation email is NOT sent to my customer

I can not reproduce this bug easily : several transactions using the same parameters (product, test credit card...) may lead to successful or unsuccessful results... I don't know what causes this.
Any idea ?

Thank you in advance,

Hello,

Anyone has an idea on how to solve this issue ?

Thank you in advance,