On Sun, Aug 23, 2015 at 1:16 PM, Johannes Löthberg <johannes@xxxxxxxxxxxx> wrote: > On 23/08, René Scharfe wrote: >> Eric, hope you see this reply on the list. Direct replies to >> sunshine@xxxxxxxxxxxxxx are rejected by my mail provider on submit in >> Thunderbird with the following message: >> >> Requested action not taken: mailbox unavailable >> invalid DNS MX or A/AAAA resource record. >> >> And with this one when using their web interface: >> >> A message that you sent could not be delivered to one or more of >> its recipients. This is a permanent error. The following address >> failed: >> >> "sunshine@xxxxxxxxxxxxxx": >> no valid MX hosts found >> >> It seems web.de wants you to get an AAAA record before I'm allowed to send >> mails to you. > > Just an A record would be enough. The issue is that mail.sunshineco.com has > neither an A nor an AAAA record, it is a CNAME to sunshineco.com, which is > invalid according to RFC2181. Interestingly, the default configuration for all domains managed by this service provider is for the mailhost to be a CNAME. While the restriction in section 10.3 of RFC2181 makes sense as a way to avoid extra "network burden", in practice, email services seem to be pretty relaxed about it, and follow the CNAME indirection as needed. I suppose it's possible that web.de is being extra strict (although it seems that such strictness would be painful for its users), or this could just be a temporary DNS lookup failure. It's hard to tell based upon the errors René reported. I did change the CNAME to an A just in case, though who knows how long it will take for the change to propagate over to web.de's server. -- To unsubscribe from this list: send the line "unsubscribe git" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html