Solved MX record of www.freebsd.org seems weird to me

M

mamalos

Hey everybody,

I wanted to test my DNS configuration and ran:

Code: 
$ host www.freebsd.org
www.freebsd.org is an alias for wfe0.ysv.freebsd.org.
wfe0.ysv.freebsd.org has address 8.8.178.110
wfe0.ysv.freebsd.org has IPv6 address 2001:1900:2254:206a::50:0
wfe0.ysv.freebsd.org mail is handled by 0 .

What made me wonder was the MX record of wfe0.ysv.freebsd.org. Is it correct to have '.' as an MX record? And if so, then what does it mean?
 
Because it's not a mail domain. This simply prevents people from trying to mail to it.
 
If they didn't have an MX record at all, would SMTP use the A record instead? Because if not, then no MX record would just suffice, wouldn't it?

But then again, why should someone use a bogus MX record just to say that they don't want to receive mails. Isn't that superfluous? No MX record should suffice, indeed.

I assume that it is just to confuse spammers who consult MX records and follow them without evaluating them first. In this scenario, it makes sense (the host avoids connections on the already closed/filtered port 25, hence saving traffic :)).
 
Yeah, you may be right. I've never created MX records like this. But it makes sense as a spam deterrent.
 
SMTP usually falls back to an A record if an MX record doesn't exist. So I believe by putting a fake MX record in it causes the mail to just fail rather than to use the IP address of the A record instead.
 
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