Exchange Online now support Plus emailing address like GMail has for many years. So if your email address is [email protected] then you can also use the email address [email protected] to create unique email addresses for mailing list etc. It is not currently enabled by default so needs to be enabled using PowerShell. The following script will do so:

# Enable Plus Emailing in Exchange Online

# Check the ExchangeOnlineManagement module is installed and >= v2.0.4
Import-Module ExchangeOnlineManagement; Get-Module ExchangeOnlineManagement

# Install module if required
#Install-Module -Name ExchangeOnlineManagement -RequiredVersion 2.0.4-Preview2 -AllowPrerelease

# Update module if required
#Update-Module -Name ExchangeOnlineManagement

# Connect to Exchange PowerShell
Connect-ExchangeOnline -UserPrincipalName [email protected]

# Change organisational config to allow plus emailing. It is off by default.
Set-OrganizationConfig -AllowPlusAddressInRecipients $true

Currently only available for mailboxes but will be added to distribution groups soon.