Send on behalf of different domain


Our organization is currently using Exchange on-line in the cloud (office 365).

We have an external vendor who would like to follow up with potential customers by sending emails on behalf of (or appear to be coming from) our organization and not theirs.

How can this be accomplished? They are running an on premise exchange system with outlook 2010 / 2013  as their client.

Can this be done by using a SPF record? If so, how?


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Vasil Michev (MVP)Commented:
You will have to add the IPs/FQDNs of their outbound servers to your SPF. For example, assuming is the IP, it should look something like this:

v=spf1 ip4: -all

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Adam BrownSr Solutions ArchitectCommented:
Probably the easiest method would be to create a mailbox in your environment for the Vendor to log into. That way you have easy control over whether or not he can actually send messages.

The other method would be for the vendor to add your domain as an accepted domain, and then for you to modify your existing SPF records (if you have any) so that their Exchange server's IP is listed on it. This technique, however, would result in the vendor's mailbox in their environment not being able to receive mail at that address, which may be a problem.

The issue here is that he will have to have a second mailbox configured somewhere in order to send messages from a different email address than his own. The easiest way to do this is to create it in O365. It's possible to make things work with the mailbox in his environment, but doing so is cludgy at best and a security risk at worst.

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Scott CSenior EngineerCommented:
Creating additional mailboxes is the only solution that uses multiple domains natively.

The bottom line is that Exchange doesn't support selecting different sending as email addresses.
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mbudmanAuthor Commented:
The problem with creating a mailbox in my organization is that the external person who has access to the mailbox can see the calendars (even though it is just availability and not details) of every single employee who works within the company.

I do not see a way around this unless someone knows of a way to limit calendar sharing within the organization.
Adam BrownSr Solutions ArchitectCommented:
You can use powershell to set prevent calendar visibility for the vendor like this:

$mailboxes = get-mailbox | where {$_.primarysmtpaddress -notlike ""}
foreach ($mailbox in $mailboxes)
   $user = $mailbox.samaccountname
   add-mailboxfolderpermission -identity $user:\calendar -user -accessrights none

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This will set things so that the vendor has no visibility on calendars in the organization. You would need to make sure to set this permission on new accounts, but this is probably easier to manage than letting the vendor use your domain as an accepted domain in their own exchange environment.
mbudmanAuthor Commented:
Thank you for your assistance.
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