Add to trigger events an email or message having been sent

There needs to be a trigger to send an email or SMS in the event of another email or SMS message having been sent.

One big reason is that hosts often need to notify guests by SMS that they have sent them an email message and to check their spam or junk folder or notify the host if they don't see it.

Perhaps the most crucial email messages needing to go out and be seen by guests are those that provide their lock code and check-in instructions. Being able to have the followup SMS triggered automatically with the sending of that email message guarantees that the SMS gets sent instead of the host forgetting to send it.