Backup MX - DNS "Fallback"
Today I tried setting up a MX backup server running ISPConfig.
I just created a regular "ISPConfig mailserver" and configured the mail transport according to posts found in the forums here, as well as relay access.
However I don't get the point on how to configure the DNS.
I have MX 1 with Prio. 10 and MX 2 with Prio. 20 as well as a CNAME mail.domain.tld pointing to MX 1.
Sending mails through MX 1 FQDN or CNAME works well.
Sending through domain.tld (without mail CNAME) doesn't work (no SMTP server found).
So MX 2 doesn't work at all.
Is their something I have to do with the DNS? Normally, it should work sending mails "to" domain.tld as it's suposed to lookup the MX records, or do I miss understand this?
Thanks for your help!