Add timeouts to outgoing SMTP mail

I wasn't able to test if this actually fixes the problem we're running into since it's hard to simulate an unresponsive SMTP server. At the very least, these timeouts seem reasonable and shouldn't hurt anything except very slow SMTP servers.
I believe this is a separate timeout, having to do with keeping the socket open after a successful send. I set it to 60s for safety, but I'm not sure it will affect much. The default is normally 1 hour. See https://github.com/andris9/simplesmtp#connection-options