[Pkg-exim4-users] Problems concerning IPv6 Port 25's opening to the Internet

Satoru Otsubo trnsnt at otip.jp
Wed Oct 31 18:22:54 UTC 2012

Thank you for offer.

> Please do not obfuscate the IP address. I would have been able to
> tcptraceroute to your host if you hadn't.

But, I was able to confirm that my PC's ipv6 port 25 was open as follows:

I have an acount of VPS(Virtual Private Server), which has no relation to the ISP in question. But the VPS provides only ipv4 ip address.
Therefore I installed miredo in the VPS.
# aptitude install miredo
And I used the default teredo-debian.remlab.net as ServerAddress.

(1) First I examined bendel.debian.org.
(i) Through miredo tunnel.
# nmap -6 bendel.debian.org -PN
25/tcp   open     smtp

(ii) Through the ISP
# nmap -6 bendel.debian.org
25/tcp   filtered smtp

(2) Then I examined my PC through the miredo tunnel.
It was important for the HGW to make the ipv6-icmp protocol of my PC open to the Internet, so that nmap can produce the correct result.

# nmap -6 eeee:....:ffff
25/tcp open  smtp

Therefore I have confirmed my PC's exim4 accepts both ipv4 and ipv6 correctly, and that the ISP blocks the ipv6 packets with dst port 25 passing through it towards the Internet.

By the way, in case of the smarthost having only ipv4 ip address, 
can the smarthost deal with email address having only ipv6 ip address ?


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