If your email is rejected by our email servers and you don't know why, then please read this web page. If you don't understand the contents of this page then contact your network system administrator and refer them to this page.
The email servers are configured to perform strict checks prior to receiving email messages. The primary reason for this is to reduce the amount of junk email ("spam") that we receive.
At present most mail servers on the Internet are not configured so strictly, so you may find that your email is delivered to other destinations but not to us.
Helo command rejected: Host not found
Your mail-server is identifying itself as "some name" but when our mail-server checks the name associated with your mail-server's IP address it finds "another name".
This is because your mail server is configured incorrectly. It should be fixed.
Spammers will often misconfigure their mail-server to make it difficult to trace them. Our mail-servers require that all inbound email come from mail-servers that are configured to identify themselves properly.
- As an example, take a look at three lines from our mail.log
- Feb 26 19:39:33 raccoon postfix/smtpd: connect from h-66-166-212-194.LSANCA54.covad.net[22.214.171.124]
- Feb 26 19:39:34 raccoon postfix/smtpd: NOQUEUE: reject: EHLO from h-66-166-212-194.LSANCA54.covad.net[126.96.36.199]: 450 : Helo command rejected: Host not found; proto=SMTP helo=
- Feb 26 19:39:36 raccoon postfix/smtpd: disconnect from h-66-166-212-194.LSANCA54.covad.net[188.8.131.52]
- Examine these log file entries:
- Feb 26 19:39:33
- Our server, "raccoon" receives a connection from IP address 184.108.40.206.
- "raccoon" performs a "reverse DNS lookup" for 220.127.116.11 and finds the "DNS name" to be "h-66-166-212-199.LSANCA54.covad.net"
- Feb 26 19:39:34
- The "raccoon" server rejects the email from 18.104.22.168
- The server at 22.214.171.124 tried to send "raccoon" some email.
The first step in this process is for 126.96.36.199 to send "raccoon" a "HELO" (or "EHLO") message. In that "HELO" (or "EHLO") message the mail-server (188.8.131.52) must identify itself.
The mail-server at 184.108.40.206 identified itself as "chef.orbitsystems.com" (call it the "HELO name") Our mail server, "raccoon", notes the discrepency between the "DNS name" (h-66-166-212-199.LSANCA54.covad.net) and the "HELO name" (chef.orbitsystems.com) and rejects the email
Feb 26 19:39:36
Our server, "raccoon", disconnects from 220.127.116.11
A "soft rejection" is used because the mismatch might be due to the fact that the other mail-server's name changed, but the DNS entry has not yet been updated, or perhaps old information is being supplied from a cache. The soft rejection allows retries to occur until DNS cache is renewed or other temporary name conflicts are resolved. So initially the sender will receive notification that the mail was not sent, but an attempt to deliver will continue for some time. However, if the mail servers "HELO name" does not match the reverse DNS query, then eventually the retries will expire and a hard rejection will result at which time the sender will get an undeliverable message.
Why this is Important
The "HELO name" is set by the person who configured the mail-server-software. The "DNS name" is set by the Internet Provider or network systems administrator. Often it is the same person, but sometimes not.
A person who wants to send junk email (a "spammer") might get a DSL line and then setup a computer with mail-server-software. His Internet Provider might not allow the sending of "spam messages", so to confuse the end-user the spammer will configure his mail-server-software to identify itself as something other than the DNS name. When an end-user receives such junk mail and tries to complain, they complain to the "wrong party" and the spammer is free to keep sending junk email for awhile longer.
Not every server that is misconfigured is a "spam server". There are many legitimate email servers that are misconfigured. But it is difficult to differentiate between "spammers who misconfigure their mail-servers" and "legitimate mail-servers that are misconfigured because of oversight". Scientific Solutions mail-servers will not accept email from misconfigured mail servers.
How do I fix this problem?
Set your mail-server-software to identify itself with the same name that a "reverse DNS lookup" will provide.
What if I don't want to fix it, or my systems administrator refuses to fix it?
Highlandpiping mail-servers will not accept email from misconfigured mail servers, so your email will continue to be rejected.
You might raise the issue with somebody that it is embarrasing for your organization to have misconfigured mail servers. It is rather like passing out business cards on which your company name is misspelled.
As a workaround you can print and send your message by US Postal Service, or send by fax.
Additional log entries for your convenience
Here are some more log entries to help specific companies that have misconfigured mail-servers.
Connection from IP 18.104.22.168
"HELO name" is dmzhpu02.cpco.com
DNS Query for IP 22.214.171.124 returns "DNS Name" mailout.cmsenergy.com
"dmzhpu02.cpco.com" does not match "cmsenergy.com" and so the mail is rejected
Feb 26 21:34:00 raccoon postfix/smtpd: connect from mailout.cmsenergy.com[126.96.36.199]
Feb 26 21:34:03 raccoon postfix/smtpd: NOQUEUE: reject: EHLO from mailout.cmsenergy.com[188.8.131.52]: 450 :Helo command rejected: Host not found; proto=SMTP helo=
Feb 26 21:34:04 raccoon postfix/smtpd: disconnect from mailout.cmsenergy.com[184.108.40.206]
Connection from IP 220.127.116.11
"HELO name" is nasmtp02.thcg.net
DNS Query for IP 18.104.22.168 returns "DNS Name" mail02.tycohealthcare.com
"nasmtp02.thcg.net" does not match "mail02.tycohealthcare.com" and so the mail is rejected
Feb 12 02:45:55 ei-tiger postfix/smtpd: connect from mail02.tycohealthcare.com[22.214.171.124]
Feb 12 02:45:59 ei-tiger postfix/smtpd: 72CDFB6EC9: client=mail02.tycohealthcare.com[126.96.36.199]
Feb 12 02:45:59 ei-tiger postfix/smtpd: 72CDFB6EC9: reject: RCPT from mail02.tycohealthcare.com[188.8.131.52]: 450 : Helo command rejected: Host not found; proto=ESMTP helo=
Feb 12 02:46:00 ei-tiger postfix/smtpd: disconnect from mail02.tycohealthcare.com[184.108.40.206]
This topic is discussed briefly in a book that is available at many bookstores: DNS and BIND Cookbook by Cricket Liu (O'Reilly and Associates). See page 93: "Configuring DNS So a Mail Server and the Email it Sends Pass Anti-Spam Tests"
BIND 8 for NT This webpage is useful for understanding how mail-servers (postfix in particular) might reject your email because the mail-server sending your message is misconfigured. The discussion is applicable to any mail-server, not just "BIND 8 for NT".