I am having an issue with @att.net and @sbcglobal.net emails. I found myself blocked from sending to these domains. A very nice ATT Representative unblocked my IP for me. Thank goodness kind Sir.
Going through the config file I have noticed Domain Throttling. I want to be sure I have the right setting before my next mailing. I am hoping that this will slow sending to matching domains a bit.
@bettsr the difficulty with domain throttling is that the effect is unpredictable. It can increase dramatically the elapsed time to send a campaign. It may be better to use the ordinary throttle to increase the time between phplist sending each email.
Also, did att.net advise you on restricting the sending rate? Often repeatedly sending to non-existent email addresses can cause an email provider to block a sending IP address.