Our Linode MX records were changed awhile back to interface with Mandrill, but now we want to use Linode's default server again. I'm assuming this means we have to restore the default MX records, but I have no idea what their values were. Is there anyway to get those values?

By default, there are no MX records.

That isn't clear. You want to set your MX record(s) to the fully qualified hostname of the machine(s) that accept incoming mail.

I'm assuming our FQHN, though based on gparent's comment, perhaps this isn't even necessary? We're installing postfix/dovecot.

By default, there are no MX records because by default, no Linode receives mail.

Follow sednet's instructions.

That is incorrect. If no MX is defined, most mail clients will send the mail to the address that the domain name resolves to.

And sometimes, they try sending to the A record even when valid MX records are defined. (Strangely, since I started that thread, it hasn't happened again.)