The stable Postfix release is called postfix-2.2.x where 2=major release number, 2=minor release number, x=patchlevel. The stable release never changes except for patches that address bugs or emergencies. Patches change the patchlevel and the release date. New features are developed in snapshot releases. These are called postfix-2.3-yyyymmdd where yyyymmdd is the release date (yyyy=year, mm=month, dd=day). Patches are never issued for snapshot releases; instead, a new snapshot is released. The mail_release_date configuration parameter (format: yyyymmdd) specifies the release date of a stable release or snapshot release. Incompatibility with Postfix 2.1 and earlier ============================================ If you upgrade from Postfix 2.1 or earlier, read RELEASE_NOTES-2.2 before proceeding. Incompatibility with snapshot 20050329 ====================================== If you use TLS, you need to execute "postfix reload" because the TLS manager protocol has changed. Incompatibility with snapshot 20050328 ====================================== The logging format has changed. Postfix delivery agents now log the RFC 3463 enhanced status code as "dsn=x.y.z" where y and z can be up to three digits each. After you upgrade from Postfix 2.2 or 2.3 you need to execute "postfix reload", otherwise you will keep running the old Postfix queue manager, which gives no special treatment to the enhanced status codes that it receives from Postfix delivery agents. Major changes with snapshot 20050328 ==================================== This release introduces support for RFC 3463 enhanced status codes. For example, status code 5.1.1 means "recipient unknown". Postfix recognizes enhanced status codes in remote server replies, generates enhanced status codes while handling email, and reports enhanced status codes in non-delivery notifications. This improves the user interaction with mail clients that hide the text of error messages from users. You can, but don't have to, specify RFC 3463 enhanced status codes in the output from commands that receive mail from a pipe. If a command terminates with non-zero exit status, and an enhanced status code is present at the beginning of the command output, then that status code takes precedence over the non-zero exit status. You can, but don't have to, specify RFC 3463 enhanced status codes in Postfix access maps, header/body_checks REJECT actions, or in RBL replies. For example: REJECT 5.7.1 You can't go here from there The status 5.7.1 means "no authorization, message refused", and is the default for access maps, header/body_checks REJECT actions, and for RBL replies. If you specify your own enhanced status code, the Postfix SMTP server will automatically change a leading '5' digit (hard error) into '4' where appropriate. This is needed, for example, with soft_bounce=yes.