When you have multiple mailboxes in your Outlook profile, changes to "Rules" and "Out-Of-Office" replies only affect the primary account mailbox. If you want to change the Out-Of-Office message for another mailbox, you must login as that mailbox. This can be achieved by creating another profile.
Close Outlook by selecting File --> Exit
In Windows, click on Start --> Control Panel
Make sure you are Viewing by \Small icons\ and click on the Mail icon
Click on the Show Profiles... button
You will see an existing list of profiles. Click on the Add... button
Type a profile name (usually the mailbox name that you want to connect to, but anything you want), click OK
Select Manually Configure server settings or additional server types and click Next
Select Microsoft Exchange or compatible service, click Next
Server name is Hecate.
Remove Use cached exchange Mode.
Type the name of the account and click Check Name. If the name is recognized it will underline the name or it will give you a list of names that are close to what you wanted. Select the right one and click OK. (If you cannot see the name you wanted then hit Cancel and try a different spelling. Please note that the name has to be the one displayed in Outlook when you are emailing that mailbox).
Once the name is underlined click More Settings...
Select the Advanced tab, and remove the check mark beside Download shared folders and click OK
Click Next >
Click Finish
You should now see the new mailbox in the list of mailboxes. Take note of what mailbox is listed under Always use this profile and then select instead prompt for a profile to be used
Click OK
Now when you start up Outlook, you will see a prompt asking you which mailbox you would like to open. Most often, you probably want the default, so you can simply click on the Enter button to go into your regular profile. When you want to see the other mailbox, simply select the name from the dropdown list and click OK.
When you are ready to go back to your original profile, exit Outlook from File --> Exit, wait 5 seconds and then restart Outlook and repeat the process.
If you get tired of the prompt to select a profile, or no longer need it:
Close Outlook by selecting File --> Exit
In Windows, click on Start --> Control Panel
Make sure you are Viewing by "Small icons" and click on the Mail icon
Click on the Show Profiles... button
Select Always use this profile and then select the original default profile that you took note of above.