Sending email using a proxy address in Microsoft 365

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Vignesh Mudliar

Vignesh has been working in the IT industry for the past 10 years. His main areas of focus are Microsoft 365, Exchange Online, PowerShell, Teams, SharePoint, Microsoft 365 Security, and GoLang. Follow his weblog.

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In this article, you will get acquainted with the nitty-gritty of this feature. You will learn the reasons why it's useful to use proxies to send emails and read about some practical experiences with them.

Aliases

Aliases enable us to receive all the emails sent to the different addresses associated with a mailbox in a single mailbox. One organization may also have multiple domains; hence, an email address for that domain would be attached to the mailboxes. See this link for a detailed explanation.

What is changing with this feature?

Until now, Microsoft 365 and Exchange Online allowed users to send emails using only their primary SMTP address. So, for example, in the screenshot here, this user could only use Demo@M365tester.onmicrosoft.com to send email.

Although the user can receive emails sent to proxies, they could not use the proxies to send emails. This is what Microsoft has now changed. Now, this user will be able to send emails via its proxies. In the following section, we will see how you can achieve this in your tenants.

Example of a mailbox with one primary SMTP address and multiple proxy addresses.

Reasons for using proxies to send emails

Two reasons exist to use this features: mergers and branding.

Mergers

The most common use case is a merger. During mergers, you can have the users receive emails at both their old and new email addresses. Generally, the new email addresses are set as the primary SMTP address. However, in some cases, you might still want them to be able to send emails using their old email addresses.

In such cases, you can enable this feature in Microsoft 365, and then your users can use their old email address from their proxies to send emails. This is a handy trick, as it saves you time. Otherwise, you would have to change the primary SMTP addresses for those users.

Now, external users and clients can still send emails to their new addresses, which takes care of the branding part. Also, your users can send emails using the new address. And if, due to business requirements, they wish to send emails using their old address, they can still do so.

Branding

This is more of a fringe case; however, it may be applicable to some organizations.

During mergers, new email addresses are set as the primary SMTP addresses for the users. The company being merged might have a presence in multiple countries. In some countries, this company brand may have special business significance in the market. This may prompt them to continue using their old email addresses while communicating with their customers.

This is a special case, and the ability to send emails using proxies would be the fix here.

Behavior in Outlook on the Web (OWA)

Let's see the setup we have. There is a mailbox in my test tenant with the email addresses shown below.

The primary SMTP address is Rob@M365tester.onmicrosoft.com.

Email addresses of the mailbox to be used as an example

Now let's attempt to send an email via one of the proxies, such as Robby@abhrapratitya.co.in.

Here in OWA, you would have to display the From box when composing a new email.

How to expose the From field in OWA

Now I display the From field at the top. Here, you still see the primary SMTP address; however, you can select From > Other email address since you want to use a proxy.

Adding proxy address in Other email address in the From field in OWA

Now, you must type the proxy email address. It will then display the proxy address in the From field in the email. Here, we are using Robby@abhrapratitya.co.in as the proxy.

From address displaying the proxy address

Now, you can type the content and send it to a recipient. Below is the email received by the recipient. As you can see, the ‘From’ address is the proxy we used.

In addition, the domain used to send the email is listed as our proxy address domain. The From address observation is particularly important, as it clearly indicates the sender to the recipient.

Details at the recipients side showing the From address and mailed by fields

In addition, the message header shows the same:

Message header shows the proxy address in the From field

Replies using proxies

Let's say a user responds to an email that was sent using a proxy. Now this email would contain the proxy address in the To field even after it is delivered to the recipient. Again, this is an important marker for the user.

Replying to an email chain using the proxy address

Also, if an email is sent to the primary SMTP address of a mailbox, you can use a proxy to reply.

Here, you can see the email that was replied to contains the proxy address and domain. It also shows the first email in the chain, which was sent to the primary SMTP address.

Observation of the From field and mailed by field at the recipients side

Behavior in Outlook for the desktop client

The process of sending emails using proxies is the same in Outlook. You have to add the From field and then type the proxy email address.

Setting the From address in Outlook desktop client

The rest is the same as in OWA. I would say, though, that if you are testing this feature in Outlook, you might have to download the Offline Address book manually, since Outlook does that only once every 24–48 hours. This means the new proxy address that you added in the cloud to a mailbox to test this will not be effective in Outlook. Hence, downloading the address book fixes that minor problem.

Enabling in Exchange Online

You must connect Exchange Online PowerShell to your tenant and then run this command:

Enabling the feature of sending emails from proxies for the tenant via PowerShell

Lack of mobile support

This feature isn't available in Outlook for iOS and Android or in ActiveSync.

Positive change

In conclusion, this is a positive thing to have in Microsoft 365. The long-awaited feature is now available.