How to Check/Enable Plus Addressing in Microsoft 365 Exchange online

What is Plus Addressing? 

Plus Addressing helps to quickly create a custom email address by adding a suffix to the standard email address. In other words, Plus Addressing is a way to create disposable email addresses that are linked with the standard email address. To create a Plus Address, you can add the “+tag” suffix to the local part of your email address. 

For example: 

Standard SMTP address: <local-part>@<domain> ( [email protected])
Plus Address: <local-part>+<tag>@<domain> ([email protected])

Plus Addressing treats the “+” sign as a special indicator and ignores everything right to the “+” sign (for routing purpose) and then delivers the mail to the standard address. 

The original email address must be valid; the +tag value that you add is arbitrary, although regular character restrictions for SMTP email addresses apply (for example, no spaces). 

Plus addressing is available in Outlook. By default, plus addressing support is disabled in Exchange Online. Since Exchange Online has always supported regular email addresses that already contain the plus sign, if you enable plus addressing, these email addresses might stop working.

You can’t enable plus addressing in the Exchange admin center (EAC); you can only enable it through Exchange Online PowerShell. If your organization’s email is routed through Exchange Online to your on-premises servers, mailboxes hosted on-premises will also be able to use plus addresses.

Update according to article from 18.05.2024:
Plus addressing (also known as subaddressing) is enabled by default in Exchange Online.

Get-OrganizationConfig | fl AllowPlusAddressInRecipients

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

Using plus addresses

You can create new plus addresses by adding a new tag. You can use plus addresses as unique addresses for services that you sign up for.

As plus addresses are not aliases that are configured on the mailbox, they don’t resolve to a user’s name in Outlook clients. This results in plus addresses being easily identifiable in the To or CC fields of messages. However, there might be scenarios where you can’t use a plus address for a Microsoft service that needs to be associated with your mailbox.

To automatically identify and filter email messages that are sent to plus addresses, use Inbox rules to act on those messages. Using the condition Recipient address includes, you can specify an action for messages sent to a particular plus address, such as moving the messages to a folder.