acs_mail_nt__post_request places the message in the queue (acs_mail_queue_outgoing) and then the TCL scheduled proc acs_mail_process_queue runs throught the queue and sends the messages. The scheduled proc runs every 15 min (IIRC) by default and you should see lines in the log like:
[03/Dec/2002:20:26:22][25880.4014090][-sched:9-] Notice: Running scheduled proc acs_mail_process_queue...
[03/Dec/2002:20:26:22][25880.4014090][-sched:9-] Notice: acs-mail-queue: cleaning up
[03/Dec/2002:20:26:22][25880.4014090][-sched:9-] Notice: acs-mail-queue: done cleaning up
[03/Dec/2002:20:26:22][25880.4014090][-sched:9-] Notice: Done running scheduled proc acs_mail_process_queue.
If you're not seeing those Notices, then try restarting the server. There are
other problems with acs-mail though, so if you only need to send out simple (not multipart) messages, acs-mail-lite is a better choice.
