Hello Benoît

Put simply, we do DNS requests for MX or A records for the given sender domain, 
if either exists this check is passed.

As for the issue at hand: the DNS servers of your customer are (were) not 
properly reachable from our IP ranges or more specifically we are (were) unable 
to get the IPs for ns1.aerni.com or ns2.aerni.com. During our investigation 
this resolution has mostly recovered and we are able to resolve the domain 
properly, so this issue should now be resolved. This makes it harder though to 
pinpoint the exact cause here, to us it currently seems though that NS records 
have been changed and the old DNS servers been turned off before the TTLs of 
the old NS records had expired, so some intermediate DNS/CNS servers still had 
cached info that was now no longer working and this made the domain 
unresolvable to our servers.

As a side note: both NS entries now share a single IP and that is even the same 
IP as the mail server, this is definitely not an optimal setup, an offsite 
secondary DNS server that didn't need changing might have prevented this from 
the start.


-----Ursprüngliche Nachricht-----
Von: swinog-boun...@lists.swinog.ch [mailto:swinog-boun...@lists.swinog.ch] Im 
Auftrag von Benoit Panizzon
Gesendet: Freitag, 12. Januar 2018 10:31
An: swinog@lists.swinog.ch
Betreff: [swinog] Bluewin Error: Der MX-Eintrag fuer die Domaene aerni.com kann 
nicht verifiziert werden

Hello List

Does anyone know, how bluewin does 'verify' an MX?

The MX of our customer is prefectly reachable for sender verification but his 
emails sent 'to' bluewin recipients are getting blocked with:

MAIL FROM: <[scrubbed]@aerni.com> Unable to verify MX-Record for domain 

aerni.com mail is handled by 10 mail.aerni.com.

mail.aerni.com has address

Connected to mail.aerni.com.
Escape character is '^]'.
220 mail.aerni.com ESMTP ready.
221 mail.aerni.com closing connection
Connection closed by foreign host.
benoit@krup:~$ telnet mail.aerni.com. smtp Trying
Connected to mail.aerni.com.
Escape character is '^]'.
220 mail.aerni.com ESMTP ready.
ehlo imp.ch
250-mail.aerni.com Hello dhcp-186.imp.ch [] 250-SIZE 52428800 
250 HELP
mail from:<>
250 OK
rcpt to:<[scrubbed]@aerni.com>
250 Accepted
250 Reset OK

Mit freundlichen Grüssen

-Benoît Panizzon-
I m p r o W a r e   A G    -    Leiter Commerce Kunden

Zurlindenstrasse 29             Tel  +41 61 826 93 00
CH-4133 Pratteln                Fax  +41 61 826 93 01
Schweiz                         Web  http://www.imp.ch

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