IPv4 only server tries to relay over IPv6


#1

The title says it all. Why does my IPv4-only server try connecting to another mailserver via IPv6?

First time this has happened.

If I ping the other server the system of course fetches its IPv4 and successfully pings it.

What’s throwing off postfix?

Thanks

Full error message:

This is the mail system at host box.domain.tld. 

#################################################################### 
# THIS IS A WARNING ONLY. YOU DO NOT NEED TO RESEND YOUR MESSAGE. # 
#################################################################### 

Your message could not be delivered for more than 3 hour(s). 
It will be retried until it is 2 day(s) old. 

For further assistance, please send mail to postmaster. 

If you do so, please include this problem report. You can 
delete your own text from the attached returned message. 

The mail system 

<[palinuro@parrotsec.org](mailto:palinuro@parrotsec.org)>: connect to 
mailserver2.parrotsec.org[2a00:6d40:40:4bb0::1]:25: Network is unreachable

#2

This is an uneducated guess …

The recipient’s mail server is not responding on the IPv4 address, so mail delivery attempts the IPv6 address which is also not responding.

And it tries the first backup MX which is not responding either … and lastly the second backup MX, which is what is showing in your warning message. So, even with two backup MX servers, this domain’s email is down or just not responding …

I also noted that you pinged the servers and they ARE responding to ping’s but neither server is responding to telnet’s on port 25 or 587. Which is the port that mail needs.


#3

ok cool interesting thanks! i’ll check with their admins


#4

Who are you hosting VPS with? See if you can disable ipv6 if you do not need it.


#5

I would definitely need it but this VPS does not have IPv6 connectivity because the provider [Netsons italy] doesn’t support it yet