fabian dacunha wrote:
a) do i have to create all the existing user accounts on my existing email server to this new server cause i already hav about 300+ email users already
Depends what you want to accomplish, for the simplest of setups, no. You can (depending on the MTA of course), simply route all mail for a particular domain or host name to another system.
In postfix this is accomplished like this: (snip the usual basic config) transport_maps = hash:/etc/postfix/transport local_recipient_maps = proxy:unix:passwd.byname, $alias_maps, hash:/etc/postfix/local_recipient
then in /etc/postfix/local_recipient: @mydomain.com THIS VALUE MUST BE PRESENT BUT IS IGNORED
and in /etc/postfix/transport: mydomain.com smtp:name_of_other_smtp_server
run postmap hash:/etc/postfix/local_recipient run postmap hash:/etc/postfix/transport restart postfix and off you go.
If you want to reject mails for invalid users at the backup MX then you can probably put the user names in the local_recipient file above, create the accounts on the system, or use a distributed authentication database like SQL, LDAP etc. My preference is the above blind forward method, if the user is invalid then the server will reject it, I don't care if it sits in the queue for a few days on the backup system.
b) incase my first email server fails are the emails on the first server lost
Depends on what you mean by fail and depends if the mail on the first server is stored there or if that system simply forwards on to another host for delivery to users. If the users that read mail access it from that system, and that system bursts into flames, and the mails happen to sit on internal storage inside the system(as opposed to a NAS or a SAN) then yes mail stored on that system is lost. If the system simply crashes and needs to be rebooted then it is likely nothing is lost.
nate