I get this requested quite often so I thought I should post how to do it.
The scenario is that you have your main email account with Microsoft on Office 365/Exchange Online, say Fred@Bloggs.com, and we connect to that mailbox via Outlook and/or Outlook Web Access. We also have email accounts setup elsewhere – on Google’s Gmail for instance say Fred@Jacks.com – and you are forwarding those emails to your main Office 365 account so that you know when new mail arrives.
Usually you would have to logon to the other service to reply to the Fred@Jacks.com emails – wouldn’t it be nice if you could reply from your Fred@bloggs.com account instead? Well, you can, and it’s really easy to setup:
Firstly, I can’t verify if this works with all email providers – it does work with Gmail accounts though.
To begin with you need to setup a contact in Office 365 for the other email address – Fred@Jacks.com:
Logon as the admin user to Office 365/Exchange Online.
Goto to the Admin Centres, choose Users, select Contacts and add the email:
You will also need to add the domain to the verified domains list:
Goto Admin center, Settings, Domains.
Follow the instructions on adding a domain – you do not need to add the email DNS records in order for the domain to be used in your account. You just need to verify you own the account by adding the TXT DNS record and verifying via this portal.
Note: the adding of a domain can take up to 4 hours to complete – took only an hour in my case.
Next you need to connect to the Exchange online server using Powershell:
This article explains how to do that: https://technet.microsoft.com/en-us/library/jj984289%28v=exchg.150%29.aspx
Make sure you have issued the command to allow scripts to run:
Select ‘Y when prompted to turn scripting on.
Type in the credentials command:
$UserCredential = Get-Credential
You will be prompted for a username and password – enter you admin username and password for Office 365/Exchange Online.
Type in the session variable creation command:
$Session = New-PSSession -ConfigurationName
-Credential $UserCredential -Authentication Basic -AllowRedirection
And then issue the session import command:
Here’s a screen shot after issuing all 3 commands:
You will then see a bunch of stuff being downloaded and will eventually return to the command prompt.
You are now connected and can start issuing commands. For a list of commands available this is a good article:
You can use a command like:
To test connectivity – this will list the permissions for user Fred (Fred@Bloggs.com).
Get-RecipientPermission "Fred Bloggs"
Will list the permissions on the contact we created above – there shouldn’t be any at this stage.
To give Send As permission to the contact issue this command:
Add-RecipientPermission "Fred Bloggs" -AccessRights SendAs -Trustee "Fred"
This gives the user Fred (Fred@Bloggs.com) permission to Send As the contact “Fred Bloggs” (Fred@Jacks.com).
You may receive an error at this point along these lines:
You can't use the domain because it's not an accepted domain for your organization.
This means the domain verification and adding process has not completed yet – can take up to 4 hours for this to complete. If you continue to get this error after 4 hours then something must have gpne wrong with the domain adding process.
If all is ok you should be prompted for confirmation – select ‘Y’ to add the permission.
You should close the session properly – otherwise it will stay open – by issuing:
You can now close Powershell.
In Outlook or Outlook Web Access create a new email, make sure you can see the From: option (In Outlook if it’s not there go to the Options menu and click the From button), type in the email address you want to Send As – Fred@Jacks.com – you only need to do this once, outlook will remember it from then on and you can select it from the pull down list (however, at time of writing it was not saving it in outlook web access). Compose your message and send – if you have forwarding setup as described above you should then receive the message and note that the from address is indeed as expected: Fred@Jacks.com.
When you reply to messages received you will need to choose the from address from the pulldown – it defaults to the main mailbox from address – Fred@Bloggs.com – there is no way of changing this behaviour that I know of.