Thanks Victor, a few great tips, which I will investigate and report back on.
On 13 October 2019 20:20:05 BST, Viktor Dukhovni <postfix-us...@dukhovni.org> wrote: >On Sun, Oct 13, 2019 at 10:44:05AM -0700, mbridgett wrote: > >> I have a problem at the moment, specifically with Epic Games - who >are >> claiming that they are sending me password reset emails - but I am >never >> receiving them. >> >> I SUSPECT that some outbound mail servers may be doing some kind of >check >> (possibly a reverse DNS lookup - and of course my IP address resolves >back >> to my ISP hostname and not "my" domain as shown below: > >No, reverse DNS checks by the *sender* of email are not plausible. > >However, there are few other potential sources of trouble: > > .COM nameservers (MX query, referral): > > byteplayer.com. IN NS ns2.123-reg.co.uk. > byteplayer.com. IN NS ns.123-reg.co.uk. > > 123-reg.co.uk nameservers (MX query, zone apex alias): > byteplayer.com. IN CNAME byteplayer.dyndns.org. > > [ This could give some not-so-robust DNS clients indigestion ] > > dyndns.org (MX query, NODATA): > dyndns.org. IN SOA ns1.dyndns.org. hostmas...@dyndns.org. 2820016809 >600 300 604800 600 > > [ Some broken SMTP senders could require MX records ] > > dyndns.org (A query): > byteplayer.dyndns.org. IN A 5.68.116.33 > > dyndns.org (AAAA query): > byteplayer.dyndns.org. IN AAAA 2a02:c7f:642c:6600::1 > > [ Some SMTP senders could try to only use IPv6 ] > > $ posttls-finger -o inet_protocols=ipv4 -l none byteplayer.com > posttls-finger: Connected to byteplayer.com[5.68.116.33]:25 > posttls-finger: < 220-mail.byteplayer.com ESMTP Postfix > <...multi-second greet pause on first connection...> > posttls-finger: < 220 mail.byteplayer.com ESMTP Postfix > posttls-finger: > EHLO straasha.imrryr.org > posttls-finger: < 250-mail.byteplayer.com > posttls-finger: < 250-PIPELINING > posttls-finger: < 250-SIZE 50000000 > posttls-finger: < 250-ETRN > posttls-finger: < 250-STARTTLS > posttls-finger: < 250-ENHANCEDSTATUSCODES > posttls-finger: < 250-8BITMIME > posttls-finger: < 250-SMTPUTF8 > posttls-finger: < 250 CHUNKING > posttls-finger: > QUIT > posttls-finger: < 221 2.0.0 Bye > > [ Some SMTP senders might give up too quickly, and not get past > your postscreen greet pause. ] > > $ posttls-finger -o inet_protocols=ipv6 -l may byteplayer.com >posttls-finger: Failed to establish session to byteplayer.com via >byteplayer.com: > connect to byteplayer.com[2a02:c7f:642c:6600::1]:25: Operation timed >out > > [ You have an IPv6 address, but no SMTP server there, > that could be a problem. ] > >-- > Viktor. -- Sent from my Android device with K-9 Mail. Please excuse my brevity.
