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Office 365 Email Signatures: CANs & CAN'Ts


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As amazing as Office 365 (now Microsoft 365) is, it does not make creating and deploying email signatures easy. There are some severe drawbacks to using the in-built Office 365 email signature editor and you will have to utilize various PowerShell commands or Transport Rules in order to implement a signature across your organization.

With this in mind, let’s have a look at the top 6 things you can and can’t do with Office 365 email signatures just using a Transport Rule.

1. You CAN’T place an email signature under a reply

Now, it’s important to note that the Transport Rule feature in Microsoft 365 has a disclaimer function, not an email signature one. As far as Microsoft is concerned, this is for automatically adding plain disclaimer text only, not an HTML email signature. Any signature content is, therefore, intended to go at the very bottom of the message body.

This means that when a recipient replies to one of your emails, the signature is not going to appear under your most recent message. Instead, it will appear at the bottom of the entire conversation, under all the replies and forwards in the email chain.

2. An email signature CAN include HTML images and hyperlinks

Even though it might seem like you can only add basic text to your Office 365 email signature using a Transport Rule, you do have the ability to paste HTML images and hyperlinks into your signature.

However, you’ll need to pull the images from public web addresses as you can’t embed them directly into the signature. This means any HTML images may appear as a red ‘X’ within the signature until the recipient downloads the additional content manually.

Make sure your Office 365 email signature images aren't embedded.

Another issue that comes up frequently is signature content not displaying correctly when sending outgoing messages from a mobile device. As a smartphone or tablet composes emails in plain text by default, all of the HTML signature content can get stripped out.

One workaround for this problem is to add something in italics or bold to every email sent from a mobile device. Doing this can sometimes cause the email signature format to remain in HTML, but it is not guaranteed.

3. You CAN autocomplete email signatures with each user’s contact details

Writing %%DisplayName%%, for example, in the appropriate section of an email signature will ensure Microsoft 365 replaces it with the user’s actual display name. This ensures every email signature is automatically personalized for each user in your Microsoft 365 tenancy. A simple Google search will show you a complete list of all available email signature attributes you can include.

However, be aware that not all users will have certain contact information. You might decide you want all email signatures to include a direct dial and mobile phone number, but some users might not have a dedicated work mobile. If this is the case, some email signatures will end up with something like an ‘M:’ line next to a blank space where the mobile number is supposed to appear. To resolve this issue, you need to create separate Transport Rules dependent on the contact details within your Microsoft 365/Azure Directory.

4. You CAN have different signatures for different departments

You can setup multiple Transport Rules for your disclaimer/signature and apply them to specific distribution groups i.e. departments within your organization. So, you could have one Transport Rule in place for your sales department and another one for marketing, each with different information.

If you need to update a signature for a certain distribution group, you’ll need to do so in every Transport Rule you’ve created. You might have to carry out signature updates several times, but it’s necessary to avoid the aforementioned contact detail gaps.

Be careful about contact detail gaps in your Office 365 email signature.

5. You CAN’T test your email signatures in advance

Unfortunately, there isn’t a way to preview your completed email signature in Office 365 before it is deployed to your users. You can review the HTML code you’ve created, but the signature won’t be completed with any user’s contact details until you add it to a Microsoft 365 Transport Rule.

With this in mind, the best way to carry out email signature updates is to apply them during IT downtime or out of working hours. That way, if there’s an issue with the signature, it is less likely to appear on important email communications.

6. Email signature updates CAN take up to two hours to take effect

Microsoft has stated that changes to a Office 365 Transport Rule may not always take effect immediately. If you’re testing a new email signature design or deploying an update to all users, you may need to wait up to two hours before the new signature is ‘live’.

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