Wait is set to 0 seconds between e mails
Send Maximum is set to 300 every 1 minute
The server guys have looked at it as it was fine a week ago. I have complained as it must be something changed ( and not from our end )
The server guys say
This is something to do with PHP and how its handled on Windows. We've never seen it before and we've spent days now trying to resolve it with no luck. No changes have been made server-side and you say none code side, so we are at a total loss.
I suggest now you treat this as a new script with a code problem and attempt to deduct where the issue lies.
To do this, I would recommend you start by splitting up the recipients into smaller groups of 10 and see if one block runs slower than the others. That way we maybe able to isolate an individual group of email addresses. At that point we can split the bad group and try to isolate the problem addresses. It maybe that just a certain domain is causing the blockage. This seems likely as it must be outside of our server and your code since no changes have been made.
Please proceed with this plan and give us an update.