Alternative smtp servers

[James A Wilde]

We are looking to build a little redundancy into the mail system by
providing alternative smtp servers for our users.  I have seen references in
these postings to alternative A records, as follows:

smtp.dom.com.    IN    A    123.456.789.12
                 IN    A    123.456.789.13

Is it really as simple as that, and will a machine set up with its smtp
server set to smtp.dom.com try a random choice from these two machines?

And secondly, would the same thing work with CNAME records, as follows:

smtp.dom.com.    IN    CNAME    smtp1.dom.com.
                 IN    CNAME    smtp2.dom.com.

Thanks for your help.  Unfortunately I left the Book at home this morning.
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mvh/regards

James