sendmail problem - Helo command rejected: Host not found

Chuck Swiger cswiger at
Mon Jan 10 15:50:50 PST 2005

Srot BULL wrote:
[ ... ]
> If I am wrong, then can anyone...give me a simple explanation (simple
> please - I know that I am asking too much, but I can assure you that I
> have already bookmarked the sendmail Website and sendmail batbook is
> already in my list of books that I am planning to purchase...not yet
> though)

The simple answer is that the name your machine claims to be isn't registered 
in the DNS, which is normal for dynamic connections.  You should either relay 
all email to the mailserver your ISP should have available, or you should 
configure your MTA to masquerade as a valid domain.

The former is likely to better in terms of passing spam-sensitive mailers.

[ ... ]
>><<< 450 <>: Helo command rejected: Host not found
>><freebsd-questions at>... Deferred: 450 <>:
>>Helo command rejected: Host not found
>><<< 554 Error: no valid recipients
>>Warning: message still undelivered after 4 hours
>>Will keep trying until message is 5 days old

Yes, see the NXDOMAIN response ("no such domain"):

28-cube% dig
; <<>> DiG 9.2.2 <<>>
;; global options:  printcmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NXDOMAIN, id: 59233
;; flags: qr aa rd ra; QUERY: 1, ANSWER: 0, AUTHORITY: 1, ADDITIONAL: 0
[ ... ]


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