SOLVED IPv6 enabled sendmail does not send to domains with IPv4 only MX which results in “config error:...

I encountered a strange problem after enabling IPv6 on my sendmail. BTW, reverse resolution is fine for my domain A and AAAA wise.

Sending mail to a domain with MX A and AAAA records switched now from IPv4 to IPv6. e.g with gmail:

sm-mta[42339]: wBE9nxJl042337: to=<example@gmail.com>, ctladdr=<user@myserver> (1001/1001), delay=00:00:01, xdelay=00:00:01, mailer=esmtp, pri=30389, relay=gmail-smtp-in.l.google.com. [IPv6:2a00:1450:400c:c06:0:0:0:1b], dsn=2.0.0, stat=Sent

but sending mail to a domain with only MX A records does not take that IPv4 address for the relay but replaces it with my own servers IPv6 address which results in the "config error: mail loops back to me (MX problem?)" error.
e.g. with gmx.net:

sm-mta[42369]: wBE9oqO5042367: to=<example@gmx.net>, ctladdr=<user@myserver> (1001/1001), delay=00:00:00, xdelay=00:00:00, mailer=esmtp, pri=30390, relay=mx00.emig.gmx.net. [IPv6:myservers_IPv6_Address!!!here should be the IPv4 address of the mx00.emig.gmx.net!!!], dsn=5.3.5, stat=Local configuration error
which furthermore leads to the "loops back to me" error.

That's what I added to sendmail.mc:
DAEMON_OPTIONS(`Name=MTA-v6, Family=inet6')

How can a IPv4 and IPv6 enabled sendmail communicate with IPv4 only MX of a foreign domain? Why doesn't it resolve the MX's IPv4 address but instead uses it's own IPv6 address? DNS resolv works fine.

edited Dec 14 '18 at 13:59

asked Dec 14 '18 at 10:43

Thorsten

Is this specific to sendmail, or do you get the same output from other software, e.g. getent ahostsv6 ipv4only.arpa or getent ahostsv6 mx00.emig.gmx.net?

– grawity
Dec 14 '18 at 12:21

Thanks for the hint. Yes, it seems not to be sendmail related. It generates an IPv6 record like mx00.emig.gmx.net.myown.domain although mx00.emig.gmx.net does not have an AAAA DNS record. Will look further into it.

– Thorsten
Dec 14 '18 at 13:37

Can you reproduce this with DNS-specific tools like host or dig, or does it only happen when using the system resolver via getent? (If it's specific to the system resolver, it will be a module in /etc/nsswitch.conf.) And, most importantly, can you reproduce this with getent ahostsv6 mx00.emig.gmx.net. with the trailing dot added?

– grawity
Dec 14 '18 at 13:51

I already resolved the problem. My hostname was with with domain "hostname.my.domain" so the resolver in search for the non-existent AAAA of mx00.emig.gmx.net returned mx00.emig.gmx.net.my.domain which resolved to my local IPv6 address and sendmail tried to send the mail to itself. Thanks again a lot!!! ;-)

– Thorsten
Dec 14 '18 at 13:55

Welcome to Super User. If you resolved the problem, please post an actual answer explaining the solution, and accept it. Thanks.

– fixer1234
Dec 14 '18 at 20:42

add a comment |

I encountered a strange problem after enabling IPv6 on my sendmail. BTW, reverse resolution is fine for my domain A and AAAA wise.

Sending mail to a domain with MX A and AAAA records switched now from IPv4 to IPv6. e.g with gmail:

That's what I added to sendmail.mc:
DAEMON_OPTIONS(`Name=MTA-v6, Family=inet6')

How can a IPv4 and IPv6 enabled sendmail communicate with IPv4 only MX of a foreign domain? Why doesn't it resolve the MX's IPv4 address but instead uses it's own IPv6 address? DNS resolv works fine.

edited Dec 14 '18 at 13:59

asked Dec 14 '18 at 10:43

Thorsten

Is this specific to sendmail, or do you get the same output from other software, e.g. getent ahostsv6 ipv4only.arpa or getent ahostsv6 mx00.emig.gmx.net?

– grawity
Dec 14 '18 at 12:21

Thanks for the hint. Yes, it seems not to be sendmail related. It generates an IPv6 record like mx00.emig.gmx.net.myown.domain although mx00.emig.gmx.net does not have an AAAA DNS record. Will look further into it.

– Thorsten
Dec 14 '18 at 13:37

Can you reproduce this with DNS-specific tools like host or dig, or does it only happen when using the system resolver via getent? (If it's specific to the system resolver, it will be a module in /etc/nsswitch.conf.) And, most importantly, can you reproduce this with getent ahostsv6 mx00.emig.gmx.net. with the trailing dot added?

– grawity
Dec 14 '18 at 13:51

I already resolved the problem. My hostname was with with domain "hostname.my.domain" so the resolver in search for the non-existent AAAA of mx00.emig.gmx.net returned mx00.emig.gmx.net.my.domain which resolved to my local IPv6 address and sendmail tried to send the mail to itself. Thanks again a lot!!! ;-)

– Thorsten
Dec 14 '18 at 13:55

Welcome to Super User. If you resolved the problem, please post an actual answer explaining the solution, and accept it. Thanks.

– fixer1234
Dec 14 '18 at 20:42

add a comment |

I encountered a strange problem after enabling IPv6 on my sendmail. BTW, reverse resolution is fine for my domain A and AAAA wise.

Sending mail to a domain with MX A and AAAA records switched now from IPv4 to IPv6. e.g with gmail:

That's what I added to sendmail.mc:
DAEMON_OPTIONS(`Name=MTA-v6, Family=inet6')

How can a IPv4 and IPv6 enabled sendmail communicate with IPv4 only MX of a foreign domain? Why doesn't it resolve the MX's IPv4 address but instead uses it's own IPv6 address? DNS resolv works fine.

edited Dec 14 '18 at 13:59

asked Dec 14 '18 at 10:43

Thorsten

I encountered a strange problem after enabling IPv6 on my sendmail. BTW, reverse resolution is fine for my domain A and AAAA wise.

Sending mail to a domain with MX A and AAAA records switched now from IPv4 to IPv6. e.g with gmail:

That's what I added to sendmail.mc:
DAEMON_OPTIONS(`Name=MTA-v6, Family=inet6')

How can a IPv4 and IPv6 enabled sendmail communicate with IPv4 only MX of a foreign domain? Why doesn't it resolve the MX's IPv4 address but instead uses it's own IPv6 address? DNS resolv works fine.

sendmail

edited Dec 14 '18 at 13:59

asked Dec 14 '18 at 10:43

Thorsten

edited Dec 14 '18 at 13:59

asked Dec 14 '18 at 10:43

Thorsten

edited Dec 14 '18 at 13:59

asked Dec 14 '18 at 10:43

Thorsten

asked Dec 14 '18 at 10:43

Thorsten

asked Dec 14 '18 at 10:43

Thorsten

Is this specific to sendmail, or do you get the same output from other software, e.g. getent ahostsv6 ipv4only.arpa or getent ahostsv6 mx00.emig.gmx.net?

– grawity
Dec 14 '18 at 12:21

Thanks for the hint. Yes, it seems not to be sendmail related. It generates an IPv6 record like mx00.emig.gmx.net.myown.domain although mx00.emig.gmx.net does not have an AAAA DNS record. Will look further into it.

– Thorsten
Dec 14 '18 at 13:37

Can you reproduce this with DNS-specific tools like host or dig, or does it only happen when using the system resolver via getent? (If it's specific to the system resolver, it will be a module in /etc/nsswitch.conf.) And, most importantly, can you reproduce this with getent ahostsv6 mx00.emig.gmx.net. with the trailing dot added?

– grawity
Dec 14 '18 at 13:51

I already resolved the problem. My hostname was with with domain "hostname.my.domain" so the resolver in search for the non-existent AAAA of mx00.emig.gmx.net returned mx00.emig.gmx.net.my.domain which resolved to my local IPv6 address and sendmail tried to send the mail to itself. Thanks again a lot!!! ;-)

– Thorsten
Dec 14 '18 at 13:55

Welcome to Super User. If you resolved the problem, please post an actual answer explaining the solution, and accept it. Thanks.

– fixer1234
Dec 14 '18 at 20:42

add a comment |

Is this specific to sendmail, or do you get the same output from other software, e.g. getent ahostsv6 ipv4only.arpa or getent ahostsv6 mx00.emig.gmx.net?

– grawity
Dec 14 '18 at 12:21

Thanks for the hint. Yes, it seems not to be sendmail related. It generates an IPv6 record like mx00.emig.gmx.net.myown.domain although mx00.emig.gmx.net does not have an AAAA DNS record. Will look further into it.

– Thorsten
Dec 14 '18 at 13:37

Can you reproduce this with DNS-specific tools like host or dig, or does it only happen when using the system resolver via getent? (If it's specific to the system resolver, it will be a module in /etc/nsswitch.conf.) And, most importantly, can you reproduce this with getent ahostsv6 mx00.emig.gmx.net. with the trailing dot added?

– grawity
Dec 14 '18 at 13:51

I already resolved the problem. My hostname was with with domain "hostname.my.domain" so the resolver in search for the non-existent AAAA of mx00.emig.gmx.net returned mx00.emig.gmx.net.my.domain which resolved to my local IPv6 address and sendmail tried to send the mail to itself. Thanks again a lot!!! ;-)

– Thorsten
Dec 14 '18 at 13:55

Welcome to Super User. If you resolved the problem, please post an actual answer explaining the solution, and accept it. Thanks.

– fixer1234
Dec 14 '18 at 20:42

Is this specific to sendmail, or do you get the same output from other software, e.g. getent ahostsv6 ipv4only.arpa or getent ahostsv6 mx00.emig.gmx.net?

– grawity
Dec 14 '18 at 12:21

Thanks for the hint. Yes, it seems not to be sendmail related. It generates an IPv6 record like mx00.emig.gmx.net.myown.domain although mx00.emig.gmx.net does not have an AAAA DNS record. Will look further into it.

– Thorsten
Dec 14 '18 at 13:37

Can you reproduce this with DNS-specific tools like host or dig, or does it only happen when using the system resolver via getent? (If it's specific to the system resolver, it will be a module in /etc/nsswitch.conf.) And, most importantly, can you reproduce this with getent ahostsv6 mx00.emig.gmx.net. with the trailing dot added?

– grawity
Dec 14 '18 at 13:51

I already resolved the problem. My hostname was with with domain "hostname.my.domain" so the resolver in search for the non-existent AAAA of mx00.emig.gmx.net returned mx00.emig.gmx.net.my.domain which resolved to my local IPv6 address and sendmail tried to send the mail to itself. Thanks again a lot!!! ;-)

– Thorsten
Dec 14 '18 at 13:55

Welcome to Super User. If you resolved the problem, please post an actual answer explaining the solution, and accept it. Thanks.

– fixer1234
Dec 14 '18 at 20:42

add a comment |

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