Info for sending e-mail via SMTP is a bit sparse so I thought I'd post a tip here in case anyone else wants to do this. My email server is accessible via authenticated user, and it's not on the localhost of the web server. I host HTTP with DreamHost but I do not use their email server. The problem I was trying to solve was that emails generated with sendmail, or from unauthenticated users, would be delivered with the From like "email@example.com on behalf of MySiteName [firstname.lastname@example.org]". That's completely unacceptable. So here is how I changed that in config.php:
$config['mail']['backend'] = 'smtp';
$config['mail']['params'] = array(
'host' => 'smtp.mydomain.com',
'port' => 2525,
'auth' => true,
'username' => 'email@example.com',
'password' => 'thepassword'
$config['mail']['appname'] = 'mySNappname';
$config['mail']['check_domain'] = true;
$config['mail']['notifyfrom'] = '"MySite Status" <firstname.lastname@example.org>';
$config['mail']['domain'] = 'mydomain.com';
Now emails look very professional, not spammy or system-generated.
I was also pleased to find that emails from the site have unique headers:
There is also a MessageType "subscribe".
EDIT: Revised notifyfrom, UI here removed the email address as though it was an invalid tag.