How to configure shared mailboxes to work with CodeTwo signatures

Problem:

You want to learn how to configure Microsoft 365 shared mailboxes for use with CodeTwo Email Signatures 365.

Solution:

Microsoft 365 shared mailboxes need to be correctly configured to work with our service. For this purpose, complete the following steps:

• Configure users' delegate permissions (Send as / Send on behalf) for a shared mailbox
• Add the necessary details to a shared mailbox’s properties (Entra ID attributes)
• Include a shared mailbox in CodeTwo's scope of licensed users

Further steps depend on what type of signatures you want to use with shared mailboxes.

For Outlook (client-side) signatures (in either Outlook or combo mode), complete one additional step:

• Adjust CodeTwo Outlook add-in settings

For cloud (server-side) signatures (in either cloud or combo mode), complete two additional steps:

• Include a shared mailbox in CodeTwo's Exchange transport rule 
• Enable message copying to the Sent Items folder of a shared mailbox 

If you need further help, see this troubleshooting article.

Configure users' delegate permissions (Send as / Send on behalf) for a shared mailbox

Delegate permissions set for shared mailboxes in the Exchange admin center affect how CodeTwo cloud (server-side) signatures are added:

• The Send as permission allows users to receive a dedicated shared mailbox signature when sending emails from the shared mailbox.
• The Send on behalf permission allows users to receive their personal signatures instead.

If a user is granted both the Send as and Send on behalf permissions, the Send as permission will take precedence.

In the case of Outlook (client-side) signatures, users need to be assigned either of the two delegate permissions. For this signature type, however, the assigned permission does not determine which signature is applied. Instead, this is controlled by the CodeTwo add-in setting Change CodeTwo Outlook (client-side) signatures to match the email address in the From field. To learn more, see the Adjust CodeTwo Outlook add-in settings (Outlook signatures only) section.

Learn more about email signatures vs. delegate permissions

To grant the delegate permissions to chosen users, you need to:

1. Sign in to the Exchange admin center with your Microsoft 365 global admin or Exchange admin account.
2. Go to Recipients > Mailboxes and select a shared mailbox for which you want to configure the delegate permissions:

   1. To grant the Send on behalf permission for 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 permissions for a shared mailbox.

   2. To grant the Send as permission, 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 for a shared mailbox.

Add the necessary details to a shared mailbox's properties (Entra ID attributes)

If you plan to use placeholders in the signature template of your shared mailbox, keep in mind that shared mailboxes typically don't have contact or personal details filled in Entra ID (Azure AD). To make sure no information is missing in the signature, add the necessary details by editing the mailbox properties in the Exchange admin center or by using CodeTwo's Attributes manager. For example, to display a team name (e.g., Customer Support), you can enter it in the First Name attribute and leave the Last Name attribute empty to achieve the result shown in Fig. 3.

Fig. 3.  A sample configuration of the First name placeholder for a shared mailbox.

Include a shared mailbox in CodeTwo's scope of licensed users

A shared mailbox needs to be included in the scope of licensed users if you want to set up a separate signature for it. This scope is defined in CodeTwo Admin Panel (in the Scope & region settings). You can either include all users in your Microsoft 365 tenant or limit the scope to a selected group (Microsoft 365 group, distribution list, or security group) that includes the shared mailbox, as shown in Fig. 4. Learn more about this scope

Note that in the case of Outlook (client-side) signatures, if a user sends an email as or on behalf of a shared mailbox, no additional license is consumed for that mailbox. On the other hand, shared mailboxes whose emails are routed through the CodeTwo service to get cloud (server-side) signatures are treated as separate users and must be assigned a license. Learn more about licensing

Fig. 4. Here you can limit the scope of licensed CodeTwo users to members of a specific group only. 

If you've limited the scope of licensed users to a selected group, as shown in Fig. 4., be sure your shared mailboxes are added as members of this group. Here's how to do that:

1. Sign in to the Exchange admin center with your Microsoft 365 global admin or Exchange admin account.
2. Go to Recipients > Groups, locate the group with the users licensed to use CodeTwo by clicking an appropriate tab (e.g., Distribution list) and click the group’s name.
3. In the pane that opens, select the Members tab and click View all and manage members (Fig. 5.).

Fig. 5. Accessing the group membership settings.

4. Click Add members and add shared mailbox(es) by using the picker.
5. When ready, click Add. The changes to the group membership will be saved.

The next steps depend on what type of signatures you want to use with shared mailboxes:

• For Outlook signatures (in Outlook or combo mode), complete the Adjust CodeTwo Signatures add-in settings step.
• For cloud signatures (in cloud or combo mode), complete the two following steps:
  • Include a shared mailbox in CodeTwo’s Exchange transport rule,
  • Enable message copying to the Sent Items folder of a shared mailbox.

Adjust CodeTwo Outlook add-in settings (Outlook signatures only)

When sending an email as or on behalf of a shared mailbox, CodeTwo can either insert a personal signature (with contact details of the user who sends the message) or a dedicated shared mailbox signature. Which signature is added depends on the CodeTwo add-in's setting Change CodeTwo Outlook (client-side) signatures to match the email address in the From field (Fig. 6.):

• If the setting is disabled (this is the default option), personal signatures will be used.
• If the setting is enabled, dedicated shared mailbox signatures will be used.

To find the add-in's setting, sign in to CodeTwo Admin Panel, select your Microsoft 365 tenant on the Tenants tab, and go to Outlook add-in. The setting is in the advanced settings section, as shown in Fig. 6. Learn more about this setting

Fig. 6. Change CodeTwo Outlook (client-side) signatures to match the email address in the From field setting in CodeTwo Admin Panel.

Note that there are some differences in how shared mailboxes are accessed in different Outlook versions. This also affects what signature is added by the CodeTwo add-in – see the table below for details.

*Provided that the Change CodeTwo Outlook (client-side) signatures to match the email address in the From field setting is disabled. Otherwise, signatures are always added based on the address entered in the From field.

Include a shared mailbox in CodeTwo's Exchange transport rule (cloud signatures only)

When you use CodeTwo in cloud or combo signature mode, you need to configure Exchange Online connectors and a transport rule in CodeTwo Admin Panel to specify users (mailboxes) whose emails are to be routed through CodeTwo's service to get signatures. You can either select all users in your Microsoft 365 tenant or limit this scope to users belonging to a selected group (a distribution list or any mail-enabled group), as shown in Fig. 7. Learn more

Fig. 7. Selecting users whose emails should go through CodeTwo to get cloud email signatures.

If you've limited the scope of senders to a selected group, as shown in Fig. 7., be sure your shared mailboxes are added as members of this group, as described here.

Enable message copying to the Sent Items folder of a shared mailbox (cloud signatures only)

If message copying is enabled for your Microsoft 365 shared mailbox, the copy of all emails sent as or on behalf of that mailbox will also be saved in the Sent Items folder of that mailbox. This allows CodeTwo's Sent Items Update (SIU) service to add signatures to emails in the shared mailbox’s Sent Items folder.

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 either type of delegate permissions:

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

   Replace <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

Which Sent Items folder is updated by CodeTwo?

If a user sends an email as a shared mailbox, the Sent Items Update (SIU) service will only update the copy of that email in the Sent Items folder of the shared mailbox (Fig. 8.). The original email in the user's Sent Items will not be updated with any signature.

Fig. 8. Send as permissions: SIU updates emails in the Sent Items of a shared mailbox.

If a user sends an email on behalf of a shared mailbox, SIU will only update the original email in the Sent Items folder of the user (Fig. 9.). The email copy in the shared mailbox's Sent Items will not be updated with any signature.

Fig. 9. Send on behalf permissions: SIU updates emails in the Sent Items of the sender.

See also:

• Troubleshooting problems with shared mailboxes
• How to create email signatures to use in emails sent from shared mailbox
• How to create email signatures to use in emails sent from group mailbox