How my mail server can get emails from the linode server?

> I use the mx backup service of linode for my domains
Presumably you meant to say that you have set up, or intend to set up a linode as a backup mail server, and now want to know how to utilise this correctly ?

If so, this will depend on which server (exim, postfix, qmail…) you're setting up…

I use postfix for my mail server, but my question is when my domain is down the domain server redirect my emails to the mx which is linode, so linode get my emails and keep it until my domain is up or online, now how my mial server can get these mails from the linode server? for example i was using uucpssh.org and they was using uucp with ssh to deliver mails to my mail server some using fetchmail ETRN option, i think now the question will be more clear.

Depends on how quickly you want your mail sent onto your primary server.

If you have your linode setup correctly as a secondary mx, it will forward onto the primary when it can. If timing is everything™ and you want to pull the mail over, try UUCP or Postfix's ETRN.

The previous poster suggests the 'right' way to do this, but if you're just dealing with occasional outages for your primary MX and the secondary MX is under your control, then one possibility is to log into the secondary and issue

postfix flush

when the primary is online, to force reasonably immediate redelivery.