Allow sending email from demo environments

[chillu]

Acceptance Criteria

• The CMS can send system emails to demo users who set up their own email address
• Emails are associated to the domains involved in the demo (silverstripe.com or silverstripe.cc)
• The chances of an email being caught as spam are low

Notes

• At the moment, it looks like those features are broken - making it especially hard to demonstrate a workflow end-to-end
• Example system emails are password resets and workflow approval notifications
• we could also use an email SaaS on the demo, we don’t have to use an SMTP relay which TSP would need to activate/implement (allow route to AWS SES etc). We’d have to a) do it from a domain that’s not under SPF/DKIM rules (silverstripe.cc?), or b) add that SaaS to it
• Might use a drop-in replacement for Mailer that routes everything through SendGrid. 100 emails a day free. https://github.com/unclecheese/silverstripe-sendgrid-mailer

[chillu]

Matt P raised that there's a security angle to allowing email sending - we need to consider phishing potential based on this (e.g. signing up with somebody else's email address and then sending a reset password email?)