Sometimes, when sending email to certain external email addresses, we have received the following undeliverable message (with actual data deleted and replaced with placeholders in <>'s):
Subject: Undeliverable: <sent message subject>
Your message did not reach some or all of the intended recipients.
Subject: <sent message subject>
Sent: 29/11/2007 14:50
The following recipient(s) could not be reached:
<person>@<company>.com on 29/11/2007 14:50
You do not have permission to send to this recipient. For assistance, contact your system administrator.
<office.ourdomain.co.uk #5.7.1 smtp;550 5.7.1 <person>@<company.com>... Relaying denied. Proper authentication required.>
We are using Office2003 and Exchange on SBS2003.
We first noticed this problem today.
Yesterday I fixed the reverse DNS, and that solved a problem about Yahoo treating our mail as spam.
Also yesterday I created an SPF record.
Also yesterday I reset the "Masquerade Domain" and "FQDN" in Exchange, to fix a Warning on DNSStuff, causesed by the SMTP Greeting not match domain name of the mailserver.
Not sure if any of this has caused the problem.
What I can say is that later we sent email to the same address and it was received fine.
Any ideas ?