Sending email is fairly simple using the acs-mail-lite package. Sending HTML email is only slightly more complicated.
set subject "my subject"
set message "<b>Bold</b> not bold"
set from_addr "me@myemail.com"
set to_addr "me@myemail.com"
# the from to html closes any open tags.
set message_html [ad_html_text_convert -from html -to html $message]
# some mailers chop off the last few characters.
append message_html " "
set message_text [ad_html_text_convert -from html -to text $message]
set message_data [build_mime_message $message_text $message_html]
set extra_headers [ns_set new]
ns_set put $extra_headers MIME-Version [ns_set get $message_data MIME-Version]
ns_set put $extra_headers Content-ID [ns_set get $message_data Content-ID]
ns_set put $extra_headers Content-Type [ns_set get $message_data Content-Type]
set message [ns_set get $message_data body]
acs_mail_lite::send \
-to_addr $to_addr \
-from_addr $from_addr \
-subject $subject \
-body $message \
-extraheaders $extra_headers