Revisit goroutines

[earaujoassis]

Goroutines are being used to send "concurrent" messages (like e-mail messages).

Resources:

• https://www.goinggo.net/2013/09/pool-go-routines-to-process-task.html
• http://nesv.github.io/golang/2014/02/25/worker-queues-in-go.html