Outlook supports subaddressing
You use plus addressing to support dynamic, disposable recipient (not sender) email addresses in your Exchange Online organization.

An SMTP email address uses the basic syntax: local-part>@<domain. For example, sean@contoso.com.

Plus addressing uses the syntax: local-part>+<tag>@<domain. For example, sean+newsletter@contoso.com.
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). For more information about using plus addresses, see the Using plus addresses section.

Using plus addresse
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. You cannot, however, send from plus addresses.

To automatically identify and filter 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. For example, you can move messages sent to a plus address to a folder.

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 limitation 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.

Note
Some web forms don't support plus signs in email addresses.
If you need to unsubscribe from an email list subscription service, some subscription services require that you use the original email address that you subscribed with. You can't unsubscribe by sending an email from a plus address.