Gilbert, Joseph wrote:
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.
We run dual-SMTP servers. Both servers are configured identically (same
alias file, same block list, same accounts) and mail on the secondary
gets shuttled over to the primary server every few minutes. Downside is
that when we setup a user, we have to set them up on both servers. The
upside is that for some of our domains, we've flipped which one is the
primary vs the backup MX. And if the primary box does die, it's a
simple internal DNS record change to point everyone at the new mail server.
We've also seen many broken MTAs deliver e-mail to the backup MX server
rather then adhering to the priority order in our MX records. Even if
the primary mail server is up, responding, and not under load.