Server-side Vs Client-side Email Signatures in Microsoft 365

Email signatures are more than just contact details. They help reinforce branding, maintain professionalism, and ensure every message carries the right business information. However, managing them in Microsoft 365 can be frustrating, as employees often forget to update them, use inconsistent formats, or may miss branding and legal disclaimers. For IT teams, maintaining consistency across the organization often turns into a time-consuming challenge.

To address this, Microsoft 365 offers two approaches: server-side and client-side email signatures. While both may look identical to recipients, they differ significantly in how they are applied, managed, and experienced. Choosing the wrong approach can lead to lack of control or poor user experience.

To understand the difference clearly, it all comes down to a simple idea on when and where the signature gets added to an email.

A server-side email signature is applied after the email is sent. Once the user sends an email, Exchange Online processes the message and evaluates the transport rules based on defined conditions. If the conditions are met, the signature is automatically appended using mail flow (transport) rules.

In Microsoft 365, this is technically implemented using disclaimer rules, which were originally designed for legal notices and confidentiality statements. Many organizations extend this capability to enforce server-side email signatures.

Since this happens at the server level, the sender does not see the signature while composing the email. It is only added during transit before the email is delivered to the recipient. This approach ensures that a consistent signature is applied across all outgoing emails in the organization, regardless of the device or app used to send them.

A client-side email signature is applied during email composition. This signature can be managed in two ways:

• User-managed client-side signature: Users create and manage their own signatures using Outlook’s built-in signature settings. This depends on how each user configures it, so it may vary from person to person. Unless a standard format is followed, signatures can look different across users, which can affect professionalism and brand consistency.
• Admin-managed client-side signature: Admins can centrally manage client-side email signatures using the PowerShell cmdlet Set-MailboxMessageConfiguration to configure mailbox-level signature settings. This approach combines central control with greater visibility during composition. However, support is currently limited to Outlook on the web (OWA) and new Outlook, and users may still be able to edit the signature while drafting.

Now that the core concept is clear, let’s look at a breakdown of how server-side and client-side email signatures differ.

If your organization’s requirements aren’t fully met by either approach alone, you can use a hybrid deployment by combining both server-side and client-side email signatures. This approach ensures a seamless, reliable signature experience across the organization.

In this model, client-side signatures allow users to preview their signature while composing emails, improving visibility during drafting. Server-side signatures then act as an enforcement layer by appending standardized branding elements or legal disclaimers after the message is sent.

The right choice ultimately depends on your organization’s priorities, whether that is centralized governance, user flexibility, or a balance of both.

Once you’ve selected the signature type that fits your organization, follow the steps below to set it up:

1. Configure server-side email signatures
2. Add user-managed client-side email signatures
3. Set up admin-managed client-side email signatures

To configure server-side email signatures, create mail flow rules in the Exchange admin center. These rules use the disclaimer feature, which is commonly used to append signatures to outgoing emails. You can configure both plain-text and HTML-based signature content.

For detailed setup instructions, follow this guide to configure email signature using transport rule.

Additionally, if you need to customize signatures based on user attributes such as username, department, or job title, you can also add supported Entra ID attributes (for example, %DisplayName%%) to the signature content.

You can also combine signatures with legal disclaimers, compliance notices, or confidentiality statements within the same mail flow rule, making it a centralized way to manage both branding and compliance requirements.

Users can create and configure their own signatures in Microsoft Outlook by following the steps below:

1. Sign in to your Microsoft Outlook account.
2. Navigate to Settings → Accounts → Signatures and select +Add signature.

   

3. Select Create. Enter your signature content and choose when it should be applied.
4. Next, click Save to apply the changes.

Once configured, the signature is automatically added when composing a new email or replying to or forwarding a message. You can also enable automatic application of a standard signature for all outgoing emails if required.

To configure admin-managed client-side email signatures in Outlook, Microsoft does not provide a direct option through the Outlook interface. Instead, you can use a PowerShell cmdlet Set-MailboxMessageConfiguration to configure mailbox-level signature settings for supported Outlook experiences. This method is currently supported only in Outlook on the web (OWA) and the new Outlook clients.

Before applying this, admins need to disable roaming signatures using the PostponeRoamingSignaturesUntilLater property. This temporarily disables Outlook’s roaming signature behavior and helps prevent conflicts across Outlook clients.

However, manually configuring signatures for every user can be time-consuming. To simplify this, you can use a PowerShell script to automate client-side signature configuration for all or list of mailboxes Outlook.

Download the script from GitHub: ConfigureEmailSignatureInOutlook.ps1

The script supports both plain text and HTML-based signatures and helps maintain a standardized email experience across the organization.

While email signatures in Microsoft 365 are highly useful, there are a few limitations to be aware of.

• Duplicate signatures issues: If a user configures a client-side signature and a server-side signature is also applied, there is a possibility of both signatures appearing in the same email.
  Note: When server-side signatures are enabled, users should avoid configuring personal Outlook signatures to avoid such duplicates.
• Server-side signatures are always added at the bottom of the email thread: When you reply to a message, you would expect the signature to appear directly under your response. However, with server-side signatures, the signature is added at the very end of the entire email conversation.
  To avoid this, go to Exchange admin center → Mail flow → Rules and open the signature rule. Under Exceptions, select Subject or body includes any of these words and add unique words from the signature.
• HTML rendering issues: Email signatures created using HTML may not always render consistently across different devices or email clients. This can result in broken images, font mismatches, or alignment issues.

Wrapping Up

That’s all! We hope this blog has given you a clear understanding of server-side vs. client-side email signatures in Microsoft 365. With this knowledge, evaluate your organization’s needs and choose the approach that best fits, rather than selecting one at random. Have questions or experiences to share? Feel free to drop them in the comments below. We’d love to hear from you. Stay tuned for more upcoming blogs.