PHP List can handle sending to zillions of email addresses, but your hosting company and/or ISP and/or the spam police won’t be as thrilled with the idea. Also, when you click Process Queue you should really keep that process window open until it’s done, but it might get stuck in the process. Meet throttle processes. [...]

If you have those ingredients, it’s a potential recipe for disaster if you’re trying to send email. Found the answer here. It basically says change “smtp.sbcglobal.yahoo.com” to “smtp.sbcglobal.net”. Found another idea here that says to use a ” % ” in place of the ” @ ” in the authentication part of the email set [...]