... and pass it to Transport.notify_flip().
This allows us to pass flip-specific information (the flip timestamp,
the new status) to transport classes.
If settings.EMAIL_MAIL_FROM_TMPL is set, it will be used
as the MAIL FROM (envelope sender) address.
The EMAIL_MAIL_FROM_TMPL value should contain a "%s" placeholder.
This is intended for routing email bounce notifications to a specific
MX server. For example, if the site runs on example.com
but we want to receive bounce notifications at the mail server running
on bounces.example.com, we can set
EMAIL_MAIL_FROM_TMPL = "%s@bounces.example.com"
Experimental, may change!
Each transport class has a notify() method. This method
used to have a single argument: "check". Some transport
classes require some extra information, and we were passing
it by adding ad-hoc fields to Check objects in
hc.api.models.Channel.notify().
After this change, notify() of each transport class expects
two arguments: "check" and "notification". This is cleaner
and more explicit than stuffing extra information in the
Check object.
