Another solution mentioned on this list is for the secondary to reject
mail if the primary is on-line. Yet another is to not have a secondary
at all, given that mta's will try several days before finally
giving up
anyway. If you have an incoming mta with a reliable hosting
company, you
probably don't need a secondary (if you accept the possible delay).
The disadvantage to not having a secondary is that if your primary goes down
longer than 4 hours, senders will likely start to get warning messages. You
could extend that period of time on your secondary if you wanted to have
quieter outages.
Other than that, yeah... secondary servers are likely becoming more of a
cost than a benefit with the increased needs of combating mail abuse.
I encourage people to comment on their viewpoints on the
advantage/disadvantage of secondary mail servers. I am interested in
looking at this from a broader perspective.
Joe