How to add signatures to Microsoft 365 shared or resource mailboxes

Problem:

You would like to add email signatures to shared or resource mailboxes in Microsoft 365 (Office 365).

Solution:

CodeTwo Email Signatures 365 supports Microsoft 365 shared mailboxes. It is also possible to add a cloud (server-side) signature to messages manually sent as a resource mailbox. Follow the links below to learn more.

• Shared mailboxes
• Resource mailboxes

Shared mailboxes

Your shared mailboxes might need to be reconfigured if you want to use all features of the program. Click the links below to learn more.

• Configure a shared mailbox in Exchange Online – learn how to configure users' delegate rights (Send as / Send on behalf) and message copying in Microsoft 365 (Exchange Online), and how it relates to signatures added by the program.

Cloud (server-side) signatures

• Create a cloud signature for a shared mailbox – find out how to configure the program to add signatures to shared mailboxes and learn when signatures are added.

Outlook (client-side) signatures

• Create a dedicated Outlook signature for shared mailbox users – find out how to create an Outlook (client-side) signature rule that will provide the users with signatures for use with shared mailboxes.
• Add an Outlook signature to an email sent from a shared mailbox – find out how to add your signature when sending an email as a shared mailbox user in Outlook or Outlook on the web (OWA).

Troubleshooting

• Emails sent as a shared mailbox are not getting cloud (server-side) signatures

Configure a shared mailbox in Exchange Online

Microsoft 365 shared mailboxes need to be correctly configured if you want to use all the features of CodeTwo Email Signatures 365 (including the Sent Items Update service).

• Configure users' delegate rights (Send as / Send on behalf) to a shared mailbox
• Enable message copying to the Sent Items folder of a shared mailbox

Configure users' delegate rights (Send as / Send on behalf) to a shared mailbox

Signatures added to shared mailboxes by the CodeTwo software are based on the sender's delegate rights, as mentioned below.

To assign the delegate rights to chosen users, you need to:

1. Sign in to the Exchange admin center as a global administrator or Exchange administrator.
2. Go to Recipients > Mailboxes from the navigation menu on the left and select a shared mailbox for which you want to configure the delegate rights.
3. To add a user with the Send on behalf of right to the shared mailbox, click Send on behalf (Fig. 1.) and select the desired users with the user picker. Save your changes by clicking Save > Confirm.

Fig. 1. Configuring the Send on behalf of permissions to a shared mailbox.

3. To configure users who can Send as the shared mailbox, go to the Delegation tab, click the Edit button in the Send as section (Fig. 2.) and choose the desired users with the user picker. Save your changes by clicking Save > Confirm.

Fig. 2. Configuring the Send as permissions to a shared mailbox.

Depending on these delegate permissions, when users send emails as / on behalf of the shared mailbox, CodeTwo Email Signatures 365 working in cloud (server-side) mode adds the signature configured for this mailbox / for the original sender, respectively. Learn more

Enable message copying to the Sent Items folder of a shared mailbox

If message copying is enabled for your Microsoft 365 shared mailbox, the messages sent by users with delegate (Send as / Send on behalf) rights are copied to the Sent Items folder of the shared mailbox. This allows the CodeTwo Sent Items Update (SIU) service to update the Sent Items folder of your shared mailbox with signatures.

To configure message copying in Microsoft 365, you need to:

1. Connect to Exchange Online, as explained in this article.
2. Run the following cmdlets to allow Exchange Online to copy emails sent by delegates with both types of rights:

   Set-Mailbox <shared-mailbox-email-address> -MessageCopyForSentAsEnabled $true
   Set-Mailbox <shared-mailbox-email-address> -MessageCopyForSendOnBehalfEnabled $true
   

   replacing <shared-mailbox-email-address> in each cmdlet with the exact email address of your shared mailbox.

3. Finally, disconnect Exchange Online by running this cmdlet:

   Disconnect-ExchangeOnline

When message copying is enabled, all emails sent by users as / on behalf of your shared mailbox will be copied to the Sent Items folder of this mailbox. The CodeTwo Sent Items Update service can update these emails with signatures, depending on the senders' delegate permissions.

Create a cloud (server-side) signature for a shared mailbox

When you use cloud signatures, CodeTwo Email Signatures 365 can either add the same signature template to emails sent from both user and shared mailboxes (e.g. to ensure design consistency, avoid managing another signature rule, etc.) or create a separate rule (& template) for shared mailboxes.

In the first scenario, you simply need to edit an existing rule and add your shared mailbox to the list of conditions on the Senders tab. Keep in mind that, by default, any newly-created shared mailbox is missing values for attributes such as First name, Last Name, Phone, and so on. To avoid missing any important information from your email signatures, be sure to fill out the necessary attribute values for your shared mailbox. To do this, you can use either:

• the User attributes manager – our tool lets you fill out the values for Microsoft Entra ID (Azure Active Directory) attributes that will be used in signatures added by CodeTwo Email Signatures 365 only. The changes will not affect your Entra ID configuration. Learn more
• the Exchange admin center (EAC) – find the shared mailbox on the mailbox list, select it and click Manage contact information (Fig. 5.).

Fig. 5. Editing shared mailbox properties in EAC.

You can use the Signature preview feature in the template editor to see what your signature template looks like (Fig. 6.).

Fig. 6. Choosing the shared mailbox as a sender, you can see placeholders replaced with the details you provided.

If you want the program to add a dedicated signature to emails sent from your shared mailbox, you need to:

1. Create a new cloud (server-side) signature rule in the signature management app. Learn more
2. In the Senders step, add your shared mailbox to the list of conditions (by clicking Add > Selected senders and selecting the shared mailbox from the list), as shown in Fig. 7.

Fig. 7. Adding a shared mailbox to the conditions of a signature rule.

3. Configure the other rule settings according to your preferences.
4. Finally, go to the Design step and compose a signature for your shared mailbox (Fig. 8.).

Fig. 8. Designing a signature for a shared mailbox.

5. Click Save & Publish for your changes to take effect.

From now on, depending on the sender'sdelegate rights (Send as / Send on behalf), emails sent from this shared mailbox will be stamped with the signature you created for this mailbox or with the signature of the sender.

If you want to configure users' delegate rights to your shared mailbox, see this section.

Create a dedicated Outlook (client-side) signature for shared mailbox users

To use CodeTwo Outlook signatures when sending emails from a shared mailbox, you must first create an Outlook (client-side) signature rule that will include all users who can send messages from the shared mailbox. To do so:

1. Create a new Outlook (client-side) signature rule in the signature management app. Keep in mind that the rule name will be the same as the name of the signature template made available in Outlook. Learn more about creating Outlook signature rules 
2. In the Senders step, add all users who have been assigned Send as or Send on behalf permission to your shared mailbox(es) to the list of conditions (by clicking Add > Selected senders and selecting the shared mailbox users from the list), as shown in Fig. 11.

Fig. 11. Adding Senders to the Outlook (client-side) signature rule.

3. Go to the Logic step and unselect the Set this signature as default for new messages and Set this signature as default for replies and forwards options, as shown in Fig. 12. That way, the signature for shared mailbox will not be inserted automatically if a user uses their default signature more often.

Fig. 12. Configuring the options to set the shared mailbox signature as not the default one.

4. In the Design step, open the signature template editor by clicking the Edit signature button, and create a signature for your shared mailbox (Fig. 13.). Learn more

Fig. 13. Creating an Outlook (client-side) signature template.

5. When done, click the Save & Publish button (Fig. 14.) to apply the rule in your organization.

Fig. 14. Saving changes to an Outlook (client-side) signature rule.

Add an Outlook (client-side) signature to an email sent from a shared mailbox

CodeTwo Outlook signatures can be automatically added to emails as users type them in Outlook or OWA. However, since you’ve configured the shared mailbox signature as not the default one, your users will need to choose it manually. Follow the steps below to select the signature and send an email as a shared mailbox:

1. Click New Email.
2. Click From and select Other Email Address from the drop-down list (Fig. 15.).

Fig. 15. Sending an email from another email address.

3. In the new window, click From (Fig. 17.).

Fig. 17. Selecting a different sender.

4. Select the shared mailbox address from the contact list displayed in the new window (Fig. 18.) and click OK.

Fig. 18. Selecting a shared mailbox from the Global Contact List.

5. Click OK twice to return to the email compose window.
6. Open the CodeTwo Signatures pane (learn more) and click the Use this signature button next to your shared mailbox signature (Fig. 19.).

Fig. 19. Inserting the shared mailbox signature manually.

7. Now that everything’s ready, you can finish composing your message and finally send it from the shared mailbox address (Fig. 20.). 

Fig. 20. Message ready to be send using the shared mailbox address and signature.

Emails sent as a shared mailbox are not getting cloud (server-side) signatures

You configured CodeTwo Email Signatures 365 so that only senders belonging to a specific group (or groups) can get email signatures (as explained in the user's manual). You noticed that emails sent as your shared mailbox are not stamped with any signature.

To solve this problem, you need to check if your shared mailbox is added (as a member) to the group whose members get email signatures from CodeTwo. If not, you need to add it. You can do it in the Exchange admin center (Fig. 21.).

Fig. 21. Adding a shared mailbox as a group member.

Also, you need to open the Exchange admin center and make sure that your shared mailbox is not added as an additional group in the conditions of the CodeTwo Exchange transport rule, as shown in Fig. 22. In the example, the group Users with CodeTwo signatures contains all users who should get email signatures, and the Marketing shared mailbox was added directly to the The sender is a member of this group condition. Such a configuration is a common mistake and will not work because shared mailboxes are not treated as group objects in Microsoft Entra ID (Azure Active Directory). As a result, the condition is not fulfilled.

Fig. 22. A shared mailbox should not be added directly (as a group) to the conditions of the CodeTwo Exchange transport rule.

If your transport rule configuration is similar, you need to:

1. Remove your shared mailbox from the The sender is a member of this group condition.
2. Add the shared mailbox to a group: it can be the group with users who get email signatures (in the example above, this group is Users with CodeTwo signatures) or you can choose another group or create a new one.
3. Add the group that includes your shared mailbox as a member to the conditions of the CodeTwo transport rule.

Learn more about editing your transport rule manually

Resource mailboxes

Emails sent automatically by room and equipment mailboxes do not receive cloud (server-side) or Outlook (client-side) signatures in CodeTwo Email Signatures 365.

However, it is possible to add a cloud signature to messages manually sent as a resource mailbox. This requires taking an additional configuration step, i.e. adding that mailbox to the All Company group. This will also allow you to select a resource mailbox as a sender in the signature management app and prepare a separate signature for this mailbox if you want to.

To add a resource mailbox to the All Company group, follow the steps below:

1. Sign in to the Exchange admin center as a global administrator, Exchange administrator, group administrator, etc.
2. Go to Recipients > Groups > Microsoft 365, select the All Company group from the list, select the Members tab, and click View all and manage members (Fig. 23.).

Fig. 23. Opening the All Company group for adding members.

3. Next, click Add members, select the resource mailboxes you want to use and click Add to add the new group members (Fig. 24.). These changes take effect immediately.

Fig. 24. Adding resource mailboxes to the All Company group.

At this point, emails sent as any of the selected resource mailboxes will use the signature that is assigned to the group the mailboxes belong to.

By adding resource mailboxes to the All Company group, you make them selectable as senders in the signature management app (on the Senders tab, click Add > Selected senders, as shown in Fig. 25. and discussed in the user’s manual). This means you can now create a separate signature rule and a signature template for resource mailboxes. Learn more

Fig. 25. Selecting resource mailboxes as senders in the signature management app.

See also:

• MS Support article on how to create a shared mailbox in Microsoft 365
• MS Support article on how to add a shared mailbox to Outlook on the web (OWA)
• MS Support article on how to add a shared mailbox to Outlook for Windows