Redunant Mail Servers
Have wondered how is it possible to set this up ..
Say for domain 123.com - MX records are setup as follows :
123.com MX preference = 10, mail exchanger = mail.123.com
123.com MX preference = 20, mail exchanger = mail.backup123.com
mail.123.com internet address = 1.2.3.4
mail.backup123.com internet address = 5.6.7.8
For this setup, everything a mail is being sent to user@123.com - the mail will first be delivered to mail.123.com @ 1.2.3.4
however, in event of mail.123.com being down i.e switch off - the mail will in turn be delivered to mail.backup123.com @ 5.6.7.8
I have seen this system working ... but my question is on the setup....
What are the requirements to set this up ?
Any special requirements required for the server @ 1.2.3.4 ?
Any special requirements requred for the server @ 5.6.7.8 ?
Could any one point to the some information on this ?
How does mail accepted be mail.backup123.com @ 5.6.7.8 get routed back to mail.123.com @ 1.2.3.4 so that the user eventually gets the email ?
