Closing out threads

Maybe I'm making some assumptions about how threads work. I have a
form that, on the press of a button, starts monitoring some SMTP
connections. On occasions I make changes while the thread is running
in the background. To reload the changed options I have to exit the
function the thread is running and restart it. I have an indicator
that tells me the function is exiting. But on restart I get an
exception that, to the best of my understanding, says that the thread
is still running and cannot be restarted.

So, does the thread keep running after I exit the function? Or is
there something I should be doing to tell the thread to terminate? Do
I need to design the function to run the thread until program's end
but read flags from the UI to stop and reload options?

TIA,
Lilith
.