550 Rule imposed mailbox access for abc@a.com.au refused: user invalid


Could you please advise why external people are getting this error while they are trying to send email to us? Email address is an external distribution group with following settings.

Message Delivery Restrictions: File attached

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VB ITSConnect With a Mentor Specialist ConsultantCommented:
Do emails sent to your domain come through an email hygiene service? If so, does this hygiene service require you to 'register' email addresses? I know for example MessageLabs from Symantec requires you to register all of the email addresses that you wish to receive external emails from within their system, otherwise external emails get rejected.
VinjasAuthor Commented:
We are using Exchange 2010 and MailMarshal (Trustwave). Saying that internal users are able to send email to that email address though.
Adam FarageEnterprise ArchCommented:
Saying that internal users are able to send email to that email address though.

MailMarshal, like most mail filter services requires the user to be synced to the boundry device (this case the MailMarshal appliance). Upload or manually create a user entry for this account and you should be good.

Internal emails will not pass through mailmarshal which is why internal is working.
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VB ITSSpecialist ConsultantCommented:
If you're using MailMarshal then you'll need to add the email address for the distribution group within MailMarshal to allow it to receive external emails.
VinjasAuthor Commented:
Thanks Mate! As you said It was a rule in Mail Marshal refusing emails. I have moved the distribution group to another OU which is excluded from that rule.

Rule: Deny Messages to Invalid Addresses

This rule denies all messages to any address not listed in the 'All Employees' group.  It saves resources by preventing delivery of messages to invalid users. You may also wish to enable DHA (Directory Harvest Attack) prevention in order to deny Spammers the ability to gain information on your valid email addresses.  
NOTE: You must populate the 'All Employees' group with all your users before enabling this rule.
VB ITSSpecialist ConsultantCommented:
Excellent! So your distribution group can receive external emails now?
VinjasAuthor Commented:
Yes - All good now!
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