Yeah, we use O365 too. Plus-addressing has just been enabled by MS a few months ago. We tested the feature in general, but haven’t integrated into Zammad jet.
# log in to O365
Get-OrganizationConfig | select AllowPlusAddressInRecipients
# enable/disable the feature
Set-OrganizationConfig -AllowPlusAddressInRecipients <$true | $false>