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It seems odd that Outlook and Exchange used to make it hard to work with more than one email address in an account. It turns out that there are many good reasons to use multiple addresses or even conceal a personal address. You might be sharing a customer contact mailbox in a CRM system with several different users, working through the merger of two different companies or simply want to keep users’ contact details from leaking into the outside world when they’re working on a confidential product.

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Aliases in Exchange

Whatever the reason, giving staff more than one address is increasingly common. But until recently, Exchange made it hard to send messages using alternate identities.

Much of that was down to the design of Exchange’s mail transfer agent, the code that passes email out into the chain of mail servers that make up the internet. It was originally built to work with only one email address per user, with everything tied to that identity. If you tried to send an email using an alias, an alternative email address, it would be overwritten with the primary email address before being sent out over SMTP.

If you were using Exchange inside a business that approach is fine: Support emails would appear to come from a support alias as they’d not leave the server or the cluster. There’s a vague rationale for allowing aliases to be received but not used for sending, as users could then redirect mail by replying from their correct address.

However, email now needs to do a lot more than connect the parts of a business – it’s very much how we do business. And aliases are part of those processes, especially as email-powered tools like Microsoft 365’s Bookings service become more common

Incoming aliases have long been built into both on-premises Exchange and Exchange Online. You can give an individual user up to 400 different aliases, without affecting how much you’re charged. Aliases aren’t shared mailboxes or distribution lists: They’re individual addresses that can be used to route mail to specific mailboxes.

While you can use distribution lists to receive, route and send email, they don’t give you the same level of control as individual aliases for users and shared mailboxes. There were complex low-level techniques that let Exchange users send mail as aliases, but they required working with custom email applications that used specific SMTP commands, not the familiar Outlook.

Managing aliases in Exchange Online

Aliases for active users

It’s simple enough to add aliases using the Microsoft 365 Admin Center. If you’re using alternative domains, make sure they’re configured before adding an alias to a user.

In the Admin Center choose Active Users under Users in the navigation pane. Once this page has opened, select a user and click their name to open the user pane. Here you can choose Manage Username And Email to add an alias. You can type in any username and pick any currently configured domain. Once configured, click Save Changes to set up the alias.

Alternative domains

Alternative domains do need to be set up with all the correct DNS settings for Microsoft 365 accounts. That requires adding them to your Microsoft 365 account using the Setup tools in Admin Center.

Once you’ve added the domain, connect it to your account by verifying it with a TXT record in the domain’s DNS records before configuring MX records to send mail to the Microsoft 365 Exchange Online service. If you’re planning on sending mail through this domain, you first need to configure its SPF, DKIM and DMARC anti-spam features at your DNS host.

Corporate name change

After a corporate name change, you can set up an address like as an alias for, with mail sent to the old company name address arriving in his normal new company name account. It’s a good idea to use aliases to redirect mail sent to common nicknames into a single mailbox, so could be an alias for the more formal

Similarly, you could give team accounts aliases, so that all the possible variants of a team name, like “accountspayable,” “accounts,” “accounts.payable” and any other versions, will end up in the same mail account. It’s worth looking at your mail logs to see if there are common errors for important addresses that you can trap and reroute with an alias.

Sending mail as an alias from Outlook

A recent update to Exchange Online finally added preview support for sending messages using aliases. Initially, you need to use PowerShell to set the SendFromAliasEnabled parameter of the Set-OrganizationConfig cmdlet. When you set this, you can enable full alias support for all mailboxes; there’s currently no way to set it for individual users or groups.

Once it’s enabled, you’re using a new version of Exchange’s SMTP service. As Microsoft points out, it’s in preview for now, as there are known issues which could cause problems in some cases. On-premises Exchange doesn’t get the new feature, which will mean any on-premises users won’t be able to send using aliases yet.

Not all Exchange email clients support the new feature. Currently, it’s supported in the mobile Outlook clients on iOS and Android and in Outlook on the web. Support for desktop Outlook is due sometime in Q2 2022, but it’s yet to arrive.

On the web, you need to show the From field when composing messages, with a dropdown of the available aliases. On mobile devices, you have to manually enter an alias, but it’ll be saved for future use. When it’s released for desktop Outlook, you’ll be able to maintain a list of commonly used aliases, which should simplify picking and choosing which alias to use.

Once you’ve set up support, users should find working with aliases simple enough. Where necessary they can keep personal addresses hidden or use nicknames or alternate mail domains to ensure email gets to them no matter how it’s addressed.

Microsoft’s plan to merge the online Outlook with its desktop version should speed up delivery of features like this. One Outlook codebase across all the versions will avoid situations where different Outlooks have different implementations of the same feature or don’t have it all.

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