Re: IPv6 recap

Sam Varshavchik <[email protected]>
Newsgroups gmane.mail.imap.courier.general
Message-ID <[email protected]>
Joe Laffey writes:

> On Fri, 5 Apr 2024, Sam Varshavchik wrote:
>>
>> No, that should not be necessary.
>>
>> Double-check that the ipv4 address, for this MX, is actually reachable.
>>
>> If there are multiple IP addresses, either IPv4 or IPv6, each one is tried.  
>> If a connection to one of them fails for any reason the next one should be  
>> tried. After the connection to an IPv6 address fails Courier should then try  
>> the IPv4 address.
>>
>> Now, if both of the IP addresses are unreachable, and the IPv4 address was  
>> tried first, the logged error would be the error that was logged from the  
>> last connection attempt, and if it was the IPv6 one then you'll just see  
>> that error.
>>
>> I think that's what's happening in your case.
>
> OK. I think that must explain it. Because it turns out there was also an  
> ipv4 connectiity issue where some connections failed, including gmail. And  
> that was when we were having the problem.

By any chance: did you manually set ESMTP_PREFER_IPV6_MX=0 in the courierd  
configuration file.

The default ESMTP_PREFER_IPV6_MX=1 makes Courier try IPv6 addresses first,  
so a total connection failure will result in the error from the last  
attempted connection's IPv4 address.

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