In all honesty, in over 7 years of using avast, I have never manager to get this to work once in all the times I tried it. But I never had a freeze when testing to try and get it to work.
I don't know how you managed to get the Task Manager to end the avast Processes as the self-defence module should have intervened. So I would say there is something else in the mix.
Personally had that happened, I would just have rebooted.
I have tried once again to get this to work, Set up the Alert Target (image1), SMTP Settings, including server authentication. and clicked Test, no lockup and avast still running, bottom part of image1. I got that to work and the test email was sent and received image2. I have pretty much got that far on every test that I have done in the past.
So next using the eicar test file to force an alert (image3), this should have triggered the email alert, this failed to send as it has on every other live test that I have done.
All I can say is that the test worked and my avast didn't lock up. I am using the latest beta, so no change their either, live virus alert email test failed.