We have multiple applications that currently talk SMTP to an external MTA. The emails have arbitrary destination domains (they're emails to be sent to our users), but all from the same internal domain (firstname.lastname@example.org).
I want to set up an internal MTA (i guess with sendmail) that queues all mails, and have the internal MTA forward these emails to the external MTA, because the external MTA occasionally goes down and this causes various problems in our applications. I figure I can set up sendmail as a queuing middleware.
If the above assumptions are correct, what would the sendmail configuration look like? The 'mailertable' feature looks promising, and so does 'SMART_HOST'.
Any thoughts before I explore these possibilities?