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Goofy errors prevent some mail recipients from getting my server's messages

Posted on 2011-10-25
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Last Modified: 2013-11-10
I am running Postfix 2.7.0 on an Ubuntu virtual machine.

Mail has mostly been working, but one of my customers is getting mail bounced when she sends to certain recipients.  She forwards the messages to a GMail account just fine ... and from there to the original recipient just fine.

I think that my Postfix server must be messing up the dialog with the intended recipients' servers a little and they're rejecting it ... but that GMail is more lenient.  But I want my Postfix server to behave!

Here's one of the error messages:
<REDACTED@REDACTED.com>: host
   mail.REDACTED.com[173.199.136.122] said: 550 Access denied -
   Invalid HELO name (See RFC2821 4.1.1.1) (in reply to MAIL FROM command)

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Another:
<SOMEONE@kcaccess.com>: host mail.kconlineinc.com[216.241.132.24] said: 554
5.7.1
   Confused? 05 (in reply to MAIL FROM command)

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I'm not finding any red flags when I use http://www.mxtoolbox.com/SuperTool.aspx?action=mx%3awilliamstonconsulting.com

Well, a warning is there:
Warning - Reverse DNS does not match SMTP Banner

Could that cause it?

If not, what should I check to get this working?

thanks!
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Question by:Daniel Wilson
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by:xterm
xterm earned 800 total points
ID: 37025713
The error about Reverse DNS not matching your SMTP banner shouldn't matter too much.  It just means that the value returned by "nslookup <your IP address>" does not match the name in the welcome banner string shown when you telnet to <your IP address> on port 25.  Nobody anywhere should deny email on this basis.

The commonality is the MAIL FROM: part of the error, which sounds like perhaps a malformed return address on your customer's part, not necessarily anything to do with Postfix misbehaving.  I would suggest setting up a 'tcpdump host 216.241.132.24" and have your customer mail the kconlineinc.com address again.  Probably the best bet would be to redirect it to a capture file which you could then step through with Wireshark, and find the MAIL FROM: line so you can see what she's putting in there.  I'll bet that will yield the answer you're looking for.
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by:Daniel Wilson
ID: 37026009
setting up a 'tcpdump host 216.241.132.24"

How do I do that? Would that be in a config file somewhere?
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Expert Comment

by:xterm
ID: 37026028
No, you will need to install the program tcpdump:


$> sudo apt-get install tcpdump

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Accepted Solution

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Papertrip earned 1200 total points
ID: 37026037
As xterm said, if the receiver is rejecting mail because of a HELO/PTR mismatch, they are just doing it wrong and nothing you can do about it.

That being said, if possible you should make the HELO/A match the PTR if possible, if not you should at least make it a FQDN, not localhost.  I'm guessing your machine is still named localhost, and that myhostname isn't set in main.cf.

[root@broken ~]# telnet 216.105.147.15 25
Trying 216.105.147.15...
Connected to 216.105.147.15.
Escape character is '^]'.
220 localhost ESMTP Postfix (Ubuntu/GNU)
helo asdf.com
250 localhost

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From main.cf
# The myhostname parameter specifies the internet hostname of this
# mail system. The default is to use the fully-qualified domain name
# from gethostname(). $myhostname is used as a default value for many
# other configuration parameters.
#
#myhostname = host.domain.tld
#myhostname = virtual.domain.tld
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Author Closing Comment

by:Daniel Wilson
ID: 37028344
Thanks to both of you for the help.  Setting myhostname seems to have solved the problem!
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