> -----Original Message-----
> From: Jake Colman
> Sent: Friday, June 13, 2003 10:07 AM
> Subject: Configuring sendmail as a backup relay
> I'd like configure a backup mail server for my domain.  The 
> backup mail server is a RedHat box in another domain.  It
> would seem I need to do the following:
> 1) Create a higher numbered MX record in my domain's dns 
> entry that points to the backup mail server.


> 2) On the backup up mail server, configure sendmail.mc to 
> uncomment the line containing "FEATURE(`relay_based_on_MX')dnl".

The relay_based_on_MX feature is not needed. 

1) Add an entry to your mailertable file:

mydomain.com    esmtp:[ip of primary mail server]

2) Then add mydomain.com to /etc/mail/relay-domains.

Whatever you do... do NOT add mydomain.com to /etc/mail/local-host-names.

3) Rebuild the mailertable database and then restart sendmail

FWIW: There is a second option (this is what I do). Use the DSMTP mailer.

1) add mydomain.com to /etc/mail/mailertable:
mydomain.com    dsmtp:[ip of primary mail server]

2) add my domain.com to /etc/mail/relay-domains.

3) Rebuild the mailertable database and then restart sendmail

The difference is now sendmail will queue all e-mail for mydomain.com
instead of trying to deliver to the primary (which is down). Plus the normal
sendmail queue runs will be ignored for e-mails that were queued with the
DSMTP mailer. i.e. No DSN's are issued should your primary be down for an
extended amount of time.

There is an added step to using the DSMTP mailer. To release the queued
e-mail from the backup server, you will need to issue an ETRN against the
backup mailer server from the primary when its backup and running. I simply
have a cronjob do this once an hour. Example:

Using the supplied etrn.pl script supplied with the sendmail source... from
the primary:

etrn.pl backup.mydomain.com mydomain.com

Steve Cowles

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