We have always supported sub-addressing (or “tagging”) when receiving e-mails, by using the “+” sign. E.g. firstname.lastname@example.org. When using forwarding using an alias, up till now, this sub-address was replicated to the forwarded destination, e.g. email@example.com gets forwarded to firstname.lastname@example.org.
As from now, this behavior is changed, the sub-address is now stripped from the forwarded destination. E.g. an e-mail to email@example.com now gets forwarded to firstname.lastname@example.org. You can still use the sub-address in rules at e.g. Gmail, based on the (original) destination.
This change fixes some issues with forwards to mail-servers that don’t support sub-addressing, such as Microsoft Exchange.
Technically, this is implemented by changing the setting “propagate_unmatched_extensions” in Postfix from “canonical, virtual” to “canonical”.