> On 21. Nov 2020, at 10:44, Tassilo Philipp <tphil...@potion-studios.com> > wrote: > >> FYI, I run into the same issue with a different provider: >> relay.yourmailgateway.de which also has a large number of A records. >> >> Trying to reproduce and digging deeper now, by adding debug logs etc. > > Interesting... thanks for checking and having thought of my report. I for > myself didn't have any issues anymore, however, I barely ever receive any > mail from sfr. Also, given the random order of IPs in the DNS reply, I simply > might have had luck if it's in any case related to the IP order. I have no > evidence for, but when I was having problems, the IP in question was among > the last ones in the reply. > > I'm curious what you'll find…
FYI, after digging deeper into this, I figured out that this was an issue with the DNS forwarders/resolver I was using (unfortunately not under my control) on this particular mail server: The forwarder is not able to resolve relay.yourmailgateway.de <http://relay.yourmailgateway.de/> at all, likely due to the large number of A records 52 A + 13 AAAA records. I believe there is a limit in BIND suite (32) and OpenBSD libc (35) and others, which restricts older gethostbyname() calls with struct hostent results down to that 30-something number. Likely the used resolver was using these old/obsolete libc functions… But OpenSMTPD and filter FCrDNS and OpenBSD ASR all doing fine here, because using getaddrinfo() alike under the hood with dynamic struct addrinfo result allocation, which does not expose any such limits and resolves all 65 A and AAAA records just fine. Thanks, Regards, Joerg
