On 23/02/2012 21:41, Marc Perkel wrote:
Not sure how this can be done.
Right now I'm running a free backup MX record service. People point their high MX records to my servers and if they go down we store the email. When they come back up it's delivered.
What I want to do is have a premium service that would allow them to view through IMAP the stored email. In order to do that I would have to deliver the email locally to a dovecot server - to a single account perhaps - and they can view/forward/delete etc.
But - when their server comes back online I'd like to gather up all the delivered email stored in Maildir format and run it back into smtp for delivery.
I'm thinking it would be possible to use dsync for this? Ideally you would have to have a way to maintain a duplicate of the AUTH database, so that users could use their current passwords for accessing it (this would obviously require the approval and cooperation of whoever you are providing this service to), but this way you could store each users mail individually and provide relatively painless access (since all each user would need to know is the backup host name and their username/password).
You'd have to configure a script on your end to:
determine a reliable way to differentiate between a temp-fail situation on the primary (in which case you just act as a normal backup MX), or an extended outage (15 minutes? 1 hour? I'd probably let the customer decide this one), which would determine when you start actually taking delivery of their mail to the 'standby' server
monitor for when the primary comes back online
wait xx interval to make sure the primary stays up (again, I'd let the customer decide this, but with a sane minimum that you define)
once the primary stays up for the required interval, dsync a one way 'dump' of the stored mails, being sure to test for success - and this process would obviously have to take into account the possibility of the primary going down again in the middle of the dsync
mv successfully restored mails on the backup mx to a temp location for xx 'safety' interval 'just in case'
delete the backed-up/stored mail that has been successfully dsync'd after the safety interval has elapsed
--
Best regards,
Charles