Is it compulsory for an outgoing smtp server to have FQDN.

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Is it compulsory for an outgoing smtp server to have FQDN.

P.V.Anthony
Hi,

My postfix server was rejecting emails from the following server. I
think it is because I am using "reject_unknown_helo_hostname".

------------------ start ------------------
Nov 15 13:20:13 mail postfix/smtpd[14663]: NOQUEUE: reject: RCPT from
unknown[103.230.232.100]: 450 4.7.1 <DD1HMALPPPPT02.hmail.sg>: Helo
command rejected: Host not found; from=<fromname@fromdomain>
to=<toname@todomain> proto=ESMTP helo=<DD1HMALPPPPT02.hmail.sg>
------------------ end --------------------

 From the helo, I can see DD1HMALPPPPT02.hmail.sg. But this domain does
not resolve, as you can see bellow. So comes my question, is it
complulsory for an outgoing smtp server to have a fully qualified domain
name. With an "A" record.

If it is not complusory then my setting was too strong and I really
should remove "reject_unknown_helo_hostname".

Need advice.

-------------- start -----------------
dig DD1HMALPPPPT02.hmail.sg

; <<>> DiG 9.9.4-RedHat-9.9.4-51.el7 <<>> DD1HMALPPPPT02.hmail.sg
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NXDOMAIN, id: 9803
;; flags: qr rd ra; QUERY: 1, ANSWER: 0, AUTHORITY: 1, ADDITIONAL: 1

;; OPT PSEUDOSECTION:
; EDNS: version: 0, flags:; udp: 512
;; QUESTION SECTION:
;DD1HMALPPPPT02.hmail.sg. IN A

;; AUTHORITY SECTION:
hmail.sg. 899 IN SOA pridns.hmail.sg. hostmaster. 205 900 600 86400 900

;; Query time: 14 msec
;; SERVER: 8.8.8.8#53(8.8.8.8)
;; WHEN: Wed Nov 15 23:43:43 +08 2017
;; MSG SIZE  rcvd: 105

--------------- end ------------------

--
P.V.Anthony



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Re: Is it compulsory for an outgoing smtp server to have FQDN.

Wietse Venema
P.V.Anthony:
> If it is not complusory then my setting was too strong and I really
> should remove "reject_unknown_helo_hostname".

Using this feature wil reject non-spam email, because there are
still too many mis-configured mail servers.

        Wietse
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Re: Is it compulsory for an outgoing smtp server to have FQDN.

Noel Jones-2
In reply to this post by P.V.Anthony
On 11/15/2017 9:48 AM, P.V.Anthony wrote:

> Hi,
>
> My postfix server was rejecting emails from the following server. I
> think it is because I am using "reject_unknown_helo_hostname".
>
> ------------------ start ------------------
> Nov 15 13:20:13 mail postfix/smtpd[14663]: NOQUEUE: reject: RCPT
> from unknown[103.230.232.100]: 450 4.7.1 <DD1HMALPPPPT02.hmail.sg>:
> Helo command rejected: Host not found; from=<fromname@fromdomain>
> to=<toname@todomain> proto=ESMTP helo=<DD1HMALPPPPT02.hmail.sg>
> ------------------ end --------------------
>
> From the helo, I can see DD1HMALPPPPT02.hmail.sg. But this domain
> does not resolve, as you can see bellow. So comes my question, is it
> complulsory for an outgoing smtp server to have a fully qualified
> domain name. With an "A" record.
>
> If it is not complusory then my setting was too strong and I really
> should remove "reject_unknown_helo_hostname".

It is not required.  I used this for a while here with
warn_if_reject and it appeared to catch more legit mail than spam.



  -- Noel Jones
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Re: Is it compulsory for an outgoing smtp server to have FQDN.

@lbutlr
In reply to this post by P.V.Anthony
On 15 Nov 2017, at 08:48, P.V.Anthony <[hidden email]> wrote:
> From the helo, I can see DD1HMALPPPPT02.hmail.sg. But this domain does not resolve, as you can see bellow. So comes my question, is it complulsory for an outgoing smtp server to have a fully qualified domain name. With an "A" record.

It is not compulsory, but the *vast* majority of servers that are not configured this way are spammers. You will reject some "legitimate" mail, but it is a tiny fraction of the illegitimate mail. When I tested this, more than 98% of the warnings were from spammer sites and private-space domains (like .local).

> If it is not complusory then my setting was too strong and I really should remove "reject_unknown_helo_hostname".

You can certainly do that. You will see an increase in spam. Also, that host will be rejected by *many* servers.

> Need advice.

Contact the company and tell them if they want to send mail to you they need to use a valid hostname with a valid rDNS, if they don't fix their settings then that's on them.

--
Apple broke AppleScripting signatures in Mail.app, so no random signatures.

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Re: Is it compulsory for an outgoing smtp server to have FQDN.

P.V.Anthony
On 16/11/2017 01:20, @lbutlr wrote:

> It is not compulsory, but the *vast* majority of servers that are not configured this way are spammers. You will reject some "legitimate" mail, but it is a tiny fraction of the illegitimate mail. When I tested this, more than 98% of the warnings were from spammer sites and private-space domains (like .local).

Thank you all for replying. The answer are useful.

I will inform them about this.

P.V.Anthony


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