Not allowed to send on behalf as Exchange2010

Hi !

We have an Exchange 2010 and an old Exchange 2003 in our org.
I moved all the resource mailboxes from the old exchange 2003 to the new exchange 2010 and some users as well.

Everything runs ok, with the only thing that some users who wants to send mail from these shared mailboxes are not allowed to do this.

This happens only if they try to do it from an Outlook 2010 client
If they do the same thing but from an outlook 2003 client then works.

Extra info : both user and resource mailbox are in the Exchange 2010 maibox server

Any ideas ?
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PaulNSWConnect With a Mentor Commented:
Try opening Outlook 2010.
Click New E-Mail

Then click on the Options tab across the top.
There you should see a button called "From" under Show Fields.
Make sure that is enabled and a "From" box should appear above the "To"
Click the drop down and change the From address to the person you are Sending As

Try sending the email
Do you mean mailing lists, as I thought resource mailboxes (for room bookings and equipment were Exchange 2010 only)

If so, have you tried upgrading them using the following:

Get-DistributionGroup –ID "DistributionGroupName" | Set-DistributionGroup –ForceUpgrade

or to upgrade all Distribution Groups within an Organization

Get-DistributionGroup –ResultSize Unlimited | Set-DistributionGroup –ForceUpgrade

If it's a shared mailbox, ie 1 mailbox that multiple users have access too. Try removing and readding the permissions again.  It may take a while for the permissions to take effect though
valbamAuthor Commented:
Hi !

What i mean with resource mailbox in our case is :
One mailbox which 4 or 5 users has access to, for example the customer support department shares this mailbox.
They have their own mailbox plus this one as shared mailbox for all of them.

All the users who has access this one can send mail from it to external mail but only if they are running Outlook 2003,

If they run Outlook2010 then they are NOT allowed to send mail on behalf of..
I hope that you are with me what I mean
valbamAuthor Commented:
I will test this on the users who has the error.
I keep you up to date
valbamAuthor Commented:
thanks, I think that your tip helped !
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