> What is the difference between mail delivered and mail posted?

It's about the same. "Mail delivered" means that LISTSERV created one mail
message for a single recipient, and passed it on to the mail system. "Mail
posted via SMTP" means that LISTSERV created a bulk SMTP transaction for
multiple recipients and passed it on to the mail system. 5-10 years ago, it
was helpful to see the difference in the logs because "Mail delivered" was
much slower. When reading the logs, it was your cue that it was normal to
see a slowdown in the time stamps, and that perhaps you should reconfigure
your lists to allow the use of bulk SMTP. Today I am not sure that the
difference is that big, especially with embedded mail-merge. But this still
corresponds to two different delivery processes in the code that it is
sometimes useful to distinguish for troubleshooting purposes. But for
practical purposes, the result is the same.

  Eric