SQL Configuration Settings Being Ignored?

I am sure I'm being blind here (it wouldn't be the first time - and won't be the last time).

I have a package that retrieves some values from SQL table to allow me to dynically create an email message, so it retrieves To Addresses, From Address, Header, Body from a table, populates variables, and uses expressions to assign those to the SEND MAIL TASK.

That is working (after a bit of head/wall/banging to get my default virtual SMTP server running locally).

Now I am trying to make the SMTP Server Name dynamic. The Property SMTPConnection specifies the SMTP Connection Manager to use, and not the server, so it doesn't seem as though I can configure a property on the SEND MAIL TASK to achieve this.

Now I'm focussing on using SQL Package Configurations to try and drive this. As I see it, just like XML configurations, if you change a value in the configuration source, then when the package runs, it get's that value, and uses it.

I have change the configuration value (outside of the package). I confirm it is actually changed by running a SQL Task that gets the value from the configuration table, and view the value assigned to the variable in watches. The value returned is a different value (in my case I changed it to an invalid servername), and yet the task still runs through successfully, using the previous SMTP servername.

huh?