Hi Dominic,

what's wrong with that?

global operating companies do that for a good reason.

they use geoIP on your client address to figure out the nearest server for you and put it into the reply to your request.

you will be able to connect with much less latency than connecting to another server on another continent

sometimes dns is also used to achive some kind of loadbalancing - just to keep in mind ;-)

cheers

Ralph

----- Am 16. Sep 2019 um 15:51 schrieb Dominic Schlegel dominic.schlegel@hostpoint.ch:

Hi All

We are experiencing problems delivering mails for domains having their MX record set to mx-eu.mail.am0.yahoodns.net (for example yahoo.it, yahoo.de, yahoo.co.uk). So far we have figured out that Yahoo’s DNS servers send different responses. Depending on the DNS response we are able to establish SMTP connections. Below example shows 2 servers from their DNS that seems to accept SMTP connections:

[root@x1:~] # dig a mx-eu.mail.am0.yahoodns.net @yf2.yahoo.com +short 188.125.72.73 188.125.72.74

[root@x1:~] # telnet 188.125.72.73 25 Trying 188.125.72.73... Connected to mtaproxy1.free.mail.vip.ir2.yahoo.com.

[root@x1:~] # telnet 188.125.72.74 25 Trying 188.125.72.74... Connected to mtaproxy2.free.mail.vip.ir2.yahoo.com.

On the other hand we sometimes get other replies from the “same” (the id.server chaos record tell’s us it’s a different one) DNS server with different A records that do not accept SMTP connections:

[root@x1:~] # dig a mx-eu.mail.am0.yahoodns.net @yf2.yahoo.com +short 188.125.73.87 212.82.101.46

[root@x1:~] # telnet 188.125.73.87 25 Trying 188.125.73.87... telnet: connect to address 188.125.73.87: Operation timed out telnet: Unable to connect to remote host

[root@x1:~] # telnet 212.82.101.46 25 Trying 212.82.101.46... telnet: connect to address 212.82.101.46: Operation timed out telnet: Unable to connect to remote host

We have so far confirmed this behaviour from different AS (Hetzer, OVH). Does anybody else experiencing the same behaviour?

We have tried to contact their postmaster address and few others we found on the internet. Unfortunately so far no one was really able to help us. The Yahoo Small Business Phone Number that has been posted on this list back in October 2009 seems no longer to be in operations too. Therefore if you know how to get in touch with their technical staff that would be much appreciated.

Best Regards Dominic Schlegel

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Hi Ralph

Doing some kind of load balancing based on DNS and the geographical location is perfectly fine. I would probably also setup an anycast DNS system if our environment would be as big as Yahoo’s.

But I would definitely be making sure that all records my servers respond with are listening for the service in question. That means in this case: All A or AAAA records “referenced" by an MX entry should at least accept SMTP connections on port 25.

Or how is one supposed to deliver mails otherwise ;-) ?

Cheers, Dominic

On 16 Sep 2019, at 20:26, Ralph Krämer ralph.kraemer@vable.ch wrote:

Hi Dominic,

what's wrong with that?

global operating companies do that for a good reason.

they use geoIP on your client address to figure out the nearest server for you and put it into the reply to your request.

you will be able to connect with much less latency than connecting to another server on another continent

sometimes dns is also used to achive some kind of loadbalancing - just to keep in mind ;-)

cheers

Ralph

----- Am 16. Sep 2019 um 15:51 schrieb Dominic Schlegel dominic.schlegel@hostpoint.ch:

...

Hi All

We are experiencing problems delivering mails for domains having their MX record set to mx-eu.mail.am0.yahoodns.net (for example yahoo.it, yahoo.de, yahoo.co.uk). So far we have figured out that Yahoo’s DNS servers send different responses. Depending on the DNS response we are able to establish SMTP connections. Below example shows 2 servers from their DNS that seems to accept SMTP connections:

[root@x1:~] # dig a mx-eu.mail.am0.yahoodns.net @yf2.yahoo.com +short 188.125.72.73 188.125.72.74

[root@x1:~] # telnet 188.125.72.73 25 Trying 188.125.72.73... Connected to mtaproxy1.free.mail.vip.ir2.yahoo.com.

[root@x1:~] # telnet 188.125.72.74 25 Trying 188.125.72.74... Connected to mtaproxy2.free.mail.vip.ir2.yahoo.com.

On the other hand we sometimes get other replies from the “same” (the id.server chaos record tell’s us it’s a different one) DNS server with different A records that do not accept SMTP connections:

[root@x1:~] # dig a mx-eu.mail.am0.yahoodns.net @yf2.yahoo.com +short 188.125.73.87 212.82.101.46

[root@x1:~] # telnet 188.125.73.87 25 Trying 188.125.73.87... telnet: connect to address 188.125.73.87: Operation timed out telnet: Unable to connect to remote host

[root@x1:~] # telnet 212.82.101.46 25 Trying 212.82.101.46... telnet: connect to address 212.82.101.46: Operation timed out telnet: Unable to connect to remote host

We have so far confirmed this behaviour from different AS (Hetzer, OVH). Does anybody else experiencing the same behaviour?

We have tried to contact their postmaster address and few others we found on the internet. Unfortunately so far no one was really able to help us. The Yahoo Small Business Phone Number that has been posted on this list back in October 2009 seems no longer to be in operations too. Therefore if you know how to get in touch with their technical staff that would be much appreciated.

Best Regards Dominic Schlegel

---

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