Upon further examination of SMTP debug output I found the server was returning the following error:
> MAIL FROM:
551 Sender address is not valid for your login. Check your email program settings.
Bounce was disabled, so the "Administrator Email" was used as the "Return-path" (bounce) address. This should normally be an address on the same domain as ListMail. Some hosts, however, are slightly more restrictive.
To test further, instead of changing your "Administrator Email" I enabled "bounce.cgi", and set the "Bounce to Address" to bounce@example.com and still got the same error message.
As a final test, setting the bounce email to "events@example.com" worked. It seems that you need to set your "Bounce to Email" (bounce enabled) or "Administrator Email" (bounce disabled) to the email address of the account used for authorization, events@example.com.
Note that this (bounce/return) email address hidden from the user in the headers of the message. You can still set the "Send From Name" and "Send From Email" to what you like for each list to be use for display and replies - I have verified this and was able to send a message appearing to be from "test@hotmail.com".
In light of these restrictions you may or may not want to use a new account to authorize with ListMail.
I noticed your "Reconnect every X emails" SMTP setting was set quite low. I think you can safely raise this value to at least 200. If you send several thousand messages at a time I would set it to 500 at minimum.
It would seem that I need to fix the test mail settings and SMTP features to properly detect these errors. For the meantime, ListMail should detect further SMTP errors such as "too many messages this connection" as expected.
Regards!
