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...
Thanks!
