Plus Addressing, also known as sub addressing or tag addressing, is a feature in Exchange Online (Microsoft 365) that allows you to create custom email addresses based on your standard email address by adding a “+” symbol followed by a keyword to your email address before the “@” symbol.
For example, if your email address is email@example.com, you can create a plus address like firstname.lastname@example.org or email@example.com. This is useful when signing up for mailing lists or online services. You can use plus addresses in any email client that sends emails and you can receive emails addressed to you using plus addresses as you would normal emails.
The advantage of Plus Addressing in M365 is that Microsoft 365 recognizes this as a keyword and routes the email to your primary inbox as normal, but the tagged address allows you to triage the email using rules.
We spoke at length about using Plus Addressing to active InBox Zero in this post: GTD and InBox Zero with Microsoft Outlook