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NDR confusion

Printed From: LogSat Software
Category: Spam Filter ISP
Forum Name: Spam Filter ISP Support
Forum Description: General support for Spam Filter ISP
URL: http://www.logsat.com/spamfilter/forums/forum_posts.asp?TID=6635
Printed Date: 20 October 2017 at 3:17am


Topic: NDR confusion
Posted By: lyndonje
Subject: NDR confusion
Date Posted: 19 March 2009 at 3:15pm
Hello,

Am I getting this correct? An email is sent from SENDER to RECIPIENT, which our SF server accepts. SF attempts to pass the email to the RECIPIENTS server on IP aaa.bbb.ccc.ddd. The recipients server rejects the email, based on the RECIPIENTs address not existing.

So this would cause SF to generate and send an NDR to the SENDER, yes? But from the logs, it seems to me as though SF is trying to delivery the NDR via the RECIPIENTS server? Which does not accept the NDR is the RECIPIENTS server is not set to relay for the SENDERS address. Is this correct? Ultimately no NDR is received by the SENDER.

Thanks

03/19/09 19:05:09:321 -- (5264) EMail from SENDER to RECIPIENT --  was forwarded to aaa.bbb.ccc.ddd:25
03/19/09 19:05:09:321 -- (5264) Some recipients do not exist, sending NDR bounce to sender
03/19/09 19:05:09:321 -- (5264) EMail from: SENDER to: RECIPIENT was returned to sender - The following recipients had delivery problems: RECIPIENT --  --  --  -- The remote server said: -- 550 5.7.1 Unable to relay for RECIPIENT --
03/19/09 19:05:14:961 -- (5264) Error-email from SENDER to RECIPIENT was forwarded to aaa.bbb.ccc.ddd
03/19/09 19:05:14:961 -- (5264) There was an error sending the NDR to: SENDER The remote server said:550 5.7.1 Unable to relay for SENDER -- 



Replies:
Posted By: lyndonje
Date Posted: 19 March 2009 at 3:43pm
A little more information for you, in my spamfilter.ini I have NotificationSMTPServer= left blank. As per the comment is says it will use the Default Destination SMTP Server for NDRs.

Therefore I would expect SF to send the NDR via the DEFAULT Destination SMTP Server (the global server listed under the Settings tab), but what I assume SF is doing, is pulling the per DOMAIN Destination Server for the RECIPIENT and trying to relay the NDR through that, but the destination server will only accept emails for the RECIPIENT, and not an NDR destined for an external users (the original sender).

Does that make sense? Is my assumption correct?


Posted By: lyndonje
Date Posted: 19 March 2009 at 3:48pm
Just thinking... is this the reason why the NotificationSMTPServer option exists? To get around this problem?


Posted By: LogSat
Date Posted: 19 March 2009 at 8:02pm
lyndonje,

Yes, your interpretation is 100% correct. SpamFilter will *never* send an email directly to the internet. All emails are forwarded to your default destination SMTP server for delivery, whether they are addressed to your customers, or whether they are NDRs to be delivered to an internet user (john@yahoo.com for ex). You will thus need to ensure that your destination SMTP server allows SpamFilter's IP the ability to relay emails thru it.

Alternatively, you do have the option to use the "NotificationSMTPServer" (and relative port value) to specify another SMTP server that will be in charge of delivering the NDRs.

The reasoning behind the decision of preventing SpamFilter with the ability to relay is to do whatever we can to in turn preventing SpamFilter from becoming an open relay to due incorrect settings. Forcing the routing thru an internal server (after the emails are cleaned for spam), reduces, in our opinion, this risk.

-------------
Roberto Franceschetti

http://www.logsat.com" rel="nofollow - LogSat Software

http://www.logsat.com/sfi-spam-filter.asp" rel="nofollow - Spam Filter ISP


Posted By: yapadu
Date Posted: 19 March 2009 at 9:58pm
This is much like a problem that can occur with authenticated relay enabled I suspect (never tested it yet).

If we allow customers to authenticate and then relay messages through, it will actually take the email and forward it to the default destination SMTP server for the customers domain. Messages never go directly to the recipient email address, if I understand it correctly.

SO, if that is the case and the default destination SMTP server for the customers domain is not set to relay messages from SF's servers then the relay system would not work anyway correct? SF would accept the message after the user authenticates, and then would not be able to do anything with the email anyway.

Am I right?


Posted By: LogSat
Date Posted: 19 March 2009 at 11:08pm
SpamFilter will always forward the emails to your destination SMTP server(s). If the email is addressed to an external address, ex john@yahoo.com, your mail server should be able to route the email properly and deliver it to the yahoo.com domain. For all this to work however, you mail server must allow SF to relay. If the relaying is not allowed, your mail server will only accept emails addressed to your domains. Any internet-bound emails that SpamFilter attempts to forward to your mail server would be rejected, and thus NDRs cannot be delivered, and your internal users will not be able to use SpamFilter as their "outgoing SMTP server", as all internet-bound emails will not be able to be forwarded to your destination SMTP server for the actual delivery.

-------------
Roberto Franceschetti

http://www.logsat.com" rel="nofollow - LogSat Software

http://www.logsat.com/sfi-spam-filter.asp" rel="nofollow - Spam Filter ISP



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