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Email & Exchange Groups - Part 2

Louis-M

Another strange problem with our UTM.

The UTM is set to only accept relayed mail from our exchange transport servers. Our transport servers send connectors point to the UTM. Works well.

We have a distribution group with 10 internal users & 10 external users. If an internal user sends to the group, all email is delivered (both internally & externally)
eg joe.bloggs@ourdomain.com > distributiongroup@ourdomain.com > sends mail to everybody @ourdomain.com & @externaldomain_A.com & @externaldomain_B.com

If an external email address emails the group, the internal emails are delivered. The external emails are delivered to the UTM and some are bounced.
eg dave.bloggs@externaldomain_A.com > distributionlist@ourdomain.com > sends to everybody at @ourdomain.com & everybody@externaldomain_B.com but bounces to everybody@externaldomain_A.com

NOTE: the different external domains here A&B. Mail goes to B but is bounced to A

So exchange is handling it and forwarding it on as it should. All I get is "bounced" in the mail manager log and in the SMTP log it says:

2016:04:28-16:33:33 gw01-1 exim-out[6865]: 2016-04-28 16:33:33 1avnwb-0001mJ-2F ** paul.bloggs@externaldomain_A.uk P=<outsidesender@externaldomain_A.uk> R=dnslookup T=remote_smtp: SMTP error from remote mail server after RCPT TO:<paul.bloggs@externaldomain_A.uk>: host mail.externaldomain_A.uk [123.123.36.163]: 550 Your mail account has been blacklisted from sending e-mails. KB17293

To me, the above is telling me that the external mail server bounced this email back by saying that the outsidesender@externaldomain_A.uk is blacklisted?

or is the UTM saying that the outsidesender@externaldomain_A.uk is blacklisted?

The user certainly isn't blacklisted at his own domain nor is the UTM blacklisted as we can send mail to that user from within our domain.

So not sure what's going on here?



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    Finally got to the bottom of this one.

    The recipient mail is for a protected network. You can email into it. What we had was an internal user of this network sending to an external distribution list (which they can do) with users from this internal network in a distribution list.
    An internal user of this network cannot mail into it externally and can only send emails to internal users or external users belonging to another domain.

    So their gateways were seeing it as SPAM or a non existent address and bouncing it accordingly.

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