On 16/02/2018 12:34, Heiko Schlittermann via Exim-users wrote: > Hi
>
> some you (j*.e@t*.de) responded, but I can't answer:
>
> j*.e*@t*.de
>
> host mail.t*.de [*.*.230]
> SMTP error from remote mail server after RCPT
> TO:<j*.e*@t*.de>:
> 550 Client host rejected: reverse DNS failure-1
>
> I'm quite sure that my IP 84.19.194.3 resolves.
> Yes, it resolves to a CNAME, but this shouldn't be a problem.
>
> J*, do you have some other mean of contact?
> Or can you, for this communication, whitelist my server 84.19.194.3?
An IP *cannot* resolve to a CNAME as per RFC 1034. It must resolve to an
A-record, hence the error "reverse dns failure".
