phpmailer and 452 Too many recipients received this hour

[alsmith]

I have an application with dozens of users each with their own login and mailing list. Some list are 1000 or over. Rarely are their issues. 

Now one user has 100 or so people on their school elist that are parents that have subscribed to their newsletter.

One ISP i see a lot of 452 Too many recipients received this hour errors and emails waiting to deliver in my mail queues. 

I'm usin gphpmailer from google https://code.google.com/a/apache-extras.org/p/phpmailer/ and have even switched the classes out with another with no luck.

 

My server is a cPanel server and uses Exim thus one IP is used when sending out the emails. Mine you thousands are sent since these are schools contacting parents that have requested their newsletter. 

 

I am wondering if anyone has thoughts, other than moving to another mailing list program since that would not be possible for this application; to help with the delivery. Each email is sent currently as an individual email and no BCC or CC is used. 

 

I've contacted the ISP and they tell me that they only allow so many recipients per hour and they cannot whitelist the server IP or anything like that. It seems somehow I would need to group by ISP (email domain) then somehow batch deliver the emails but currently I use the recommended sending methods for the phpmailer when sending email from a database list. 

 

Again, it appears this is one ISP out of many across the country. (carolina.rr.com)

 

I am hoping to find a solution other than a complete rewrite and while on cPanel I am not finding any solutions there.

 

Thanks