Enable ‘+’ plus addressing in Exchange Online

One of the most requested features on Microsoft’s UserVoice forum was the Support for Dynamic ‘+’ Email Aliases in Office 365. This has been pending since 2017 and Microsoft finally implemented it in September 2020. Woohoo! However, it’s not enabled by default in Exchange Online, so we’ll have to turn it on.

What is ‘+’ plus addressing?

Plus addressing is an easy way to create many custom email addresses that all go to one mailbox. This is accomplished by adding a suffix to a standard email alias (the local-part before the @ bit).

Let’s look at an example:

Default email address – [email protected] [local-part]@[domain]

Sample ‘+’ plus address – [email protected] [local-part]+[tag]@[domain]

The plus symbol is treated as a special indicator where Exchange will ignore everything after it (up to the @ symbol) and deliver all mail to the default SMTP address. So in the example above, all mail sent to [email protected] will be delivered to [email protected]

Plus addressing and Microsoft 365

Sounds great, but why is it not enabled by default in Exchange Online? Alas, there is a good reason. The ‘+’ sign according to RFC is actually a valid part of an email address. So it’s possible that some organisations are already using it in their email addresses.

Example:

User: [email protected]

Shared mailbox: [email protected]

If plus addressing was enabled, where do you think the mail for the shared mailbox would be delivered?

Check if you have any affected email addresses

Just imagine turning on plus addressing and suddenly mail starts to go to unintended mailboxes! Before we go and enable the feature, we should check if we have any email addresses in our organization with a plus already in them.

It’s simple to do via Exchange Online PowerShell:

Connect-ExchangeOnline

Get-Recipient | Where {$_.EmailAddresses -like "*+*"}

If nothing is returned, then you’re probably fine to enable plus addressing in your tenant. Of course, you might need to take it through change control…

Enable ‘+’ email addressing via Exchange Online PowerShell

Luckily, enabling the feature is straight forward and can be done with just one line of code. However, once it’s enabled it may take some time before it takes effect across your entire tenant.

Limitations – Currently, plus addressing only works for mailboxes. Support for non-mailboxes such as groups and distribution lists will be available by the end of December 2020. See comments in the original user voice forum post (TLDR: there was a bug, so the initial feature release was scoped).

Connect-ExchangeOnline

# Check current setting to see the status
Get-OrganizationConfig | FL AllowPlusAddressInRecipients

# Enable the feature by setting AllowPlusAddressInRecipients to true
Set-OrganizationConfig –AllowPlusAddressInRecipients $true

Shout about it from the rooftops

Now that the feature is enabled, it’s time to let end-users know. Time to get the support documents updated!

If anyone has used Gmail before, then they’re probably aware of how it works. But if not, then it’s just another feature that you can to the pros list of why you’re using M365.

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