I think this would be useful for some people, myself included. I understand the desire for this sort of feature because my job and therefore general workflow is very email-centric; my inbox is open 24/7.
The only dicey thing with it is that the game uses Google Apps for Business for sending mail. This good thing about it is that it was very easy to setup and configure and there is no maintenance required from me. The bad thing about it is that I'm limited to sending 2,000 messages per day. Current usage (355 bmails per day on average over the past 90 days) falls well under this limit, but there could be outliers that make us hit the limit.
Given the sending limits and the higher priority of bigger projects right now, this probably won't happen for awhile, but I think I would like to see it happen eventually (and depending on the game's growth, it may just require delegating email sending to the bots4 server).