Most, if not all, of the Domino systems I've developed send automated emails via server-based scripts. Normally this is by creating a NotesDocument object, making sure it has a "SendTo" field and then calling the .Send() method, which routes it via the Domino SMTP task to the intended recipient.
It's always worked well but every now and then there's the inevitable support call to say "User X says they didn't get the email about Y after doing Z".
My approach to this used to be "Hey, my duties end once when I call dot send!" and I'd explain that it's an admin issue that's "out of my hands". But I now like to help out as much as I can and will do my best to work out why no mail was received while explaining that delivery of email is as reliable as Royal Mail.
What I tend to do now when sending email via script is add a BCC to a special GMail account of mine to all emails sent. If the mail is in that account then I know it was sent and that Domino routed it out of the server (at least to my address anyway). Not ideal, but it helps get to the bottom of things.
A system I'm working on at the moment is ASP.NET based and so there's no inbuilt SMTP server. Well, there is, kind of, but I chose to use GMail's SMTP server to send mail. The C# code connects, authenticates and sends the mail via a connection to a specified port at smpt.gmail.com. All works well and you can tell via Exception catching whether it went wrong or not.
An added bonus of the GMail method is that it stores a copy of the email in the sent folder of the account used to authenticate, so I always have a record of what happened and I assume that the fact it's in that folder means it was in fact sent (whether it was received or not is a different matter, of course).
In Domino I guess you could do this if you created the NotesDocument in a dedicated Notes Mail file and save it once sent? Does that mean it was delivered though? There's nothing to say it's not dead mail in mail.box.
What's your approach to sending email and fielding calls form irate users who blame you for problems with the minefield that is email delivery?