> Here is the situation, we have a primary mail server located in the
> data center of an African Operator.
> Unfortunately the internet link is not steady at all and It tends to
> fail every week for couple of hours and sometimes even for days.
> For strategical reasons this server can not be located in another
> country or in another place.
> I have setup another server (backup MX), but this does not allow our
> users to access their mail while the server is down or to post mail
> during the failed time. It only allows not to loose mail.
> I wanted to know what you suggest me as a solution to create a usable
> "emergency" server that could be used while the main server is down.
If you want the users to be able to access their mailboxes via both
servers, then you need a message store that supports replication
between the servers (when you add or delete one message in the
message store on one machine, then that message store sends an
update to the other machine to add or delete that same message;
and when a message store update cannot be sent immediately, then
it is queued and sent as soon as the link becomes available).
Such replicated database functionality is not part of Postfix, but
it could be plugged into Postfix (or any other MTA) provided that
the database has suitable interfaces. Postfix is a mail transfer
agent, not a message store manager, and SMTP can only deliver mail,
not remove it.