Add SMTP server to send emails to users (or configure external SMTP)

[spwoodcock]

Is your feature request related to a problem? Please describe.

• We need to send emails to users sometimes.

Describe the solution you'd like

• Either via external SMTP server (e.g. Google, or HOT project-wide server).
• Or we add an SMTP server as part of the FMTM stack - more user friendly.
• Environment variables must be configured to use the server.

Describe alternatives you've considered

• Push notifications, but too complex for our use case.