Microsoft’s Plus Addressing feature allows users to create an indefinite number of custom and unique email addresses by adding suffix text strings to their standard address using a ‘+’ delimiter. The feature was first announced by the company during Microsoft Ignite 2019 and roll out started in September 2020. Plus addressing is disabled by default in Exchange Online organizations, however, admins can easily toggle it on using Exchange Online PowerShell. Microsoft mentions the possibility to filter incoming emails and to keep track of marketing or sales campaigns.
Source: https://www.bleepingcomputer.com/news/microsoft/microsoft-disposable-emails-now-available-in-exchange-online/