ok, added the debug script, the results of which i have copied below. before that is the final response from the server company. i sent the test to three of my email addresses, they all got through, but were reported as failed in the test. Also, i noticed that since this error has been occurring i have not been at all receiving the Plain Text version of the test message - not sure if that has anything to do with anything.
Response from server company:
I am sorry to hear your phpList e-mails are not working properly. This appears to be phpMailer falsely stating that the messages are failing. They are being delivered properly. When I provide the SMTP server with the same commands your client is using directly it processes the e-mail and sends it correctly. Since this appears to be a coding issue with phpList or PHPMailer our ability to troubleshoot this is limited. I recommend reaching out to phpList for further assistance. [I have been trying to resolve this with the server company for quite some time.]
http://translationstop.com/erase.txt (this site blocked me from posting the error message, so I have to do it this way, sorry)
[this repeats for each of the three addresses. what concerns the message near the very top ("We do not authorize the use of this system to transport unsolicited, 220 and/or bulk e-mail."), the server company said that was a simple message but does not change anything.
Note that I use PHPMailer with some of my own scripts without any problems.]