Make mass mailing an asynchronous process.
Make mass mailing an asynchronous process.

Fixes #380.

malemburg/epcon,barrachri/epcon,malemburg/epcon,matrixise/epcon,PythonSanSebastian/epcon,EuroPython/epcon,malemburg/epcon,barrachri/epcon,PythonSanSebastian/epcon,matrixise/epcon,matrixise/epcon,barrachri/epcon,EuroPython/epcon,PythonSanSebastian/epcon,PythonSanSebastian/epcon,barrachri/epcon,barrachri/epcon,PythonSanSebastian/epcon,barrachri/epcon,artcz/epcon,artcz/epcon,matrixise/epcon,artcz/epcon,matrixise/epcon,artcz/epcon,malemburg/epcon,EuroPython/epcon,malemburg/epcon,EuroPython/epcon,PythonSanSebastian/epcon,malemburg/epcon,artcz/epcon,matrixise/epcon,artcz/epcon