Mass Mailer - how to not send the same mail more than once to users?

So Mass Mailer seems like a great module - but it has a large failing for what I would think is a typical user case.

Say you want to send a mail to each of your new members, a few days after they join.

You only want to send the mail ONCE to each user, and you are getting a few hundred new users join per day.

Great! you set up a campaign, and where you set up the email you make sure you have "One letter per one account" turned on.

Perfect! I am glad they included that option..

So you hit the send button, and then it reports back "sent to 105 users". Awesome, you think to yourself, you'll come back and run it again tomorrow.

So the next day, you go to Mass Mailer and there is no "send" button that campaign? How do you send it again...  Hmmm

SO you see "copy campaign" ok - cool - I'll copy it and send it again. Then you realise - wait if it is a new campaign, then it i going to send to the 105 users I sent it to yesterday.

The end result is to send it to the second 100 users you need to spam the first. Then to send it to the 3rd 100 users, you need to spam the first 100 a second time and then 2nd 100 a second time and so on.

So what is missing is a simple "Send Again" button on the sent campaign, that will send it to new users, because it will respect the "one letter per one account" switch.

I am sure this is how the module was meant to work when it was imagined, but it didn't turn out this way. Otherwise why would the "One letter per one account" switch even be there.

Una team, can we please have a "Send again" button on the sent Mass Mailer campaigns please?