Mail: upgrade to Dovecot 2.4 #8267

The Mail application runs Dovecot 2.3, which is no longer developed: new features and fixes go into Dovecot 2.4. Dovecot 2.4 configuration is not compatible with 2.3, so the upgrade needs a migration of every existing mail server, which must happen during the normal application update, without manual steps and without losing messages or settings.

Proposed solution

• Build the Mail application image with Dovecot 2.4 and rewrite its configuration for the new syntax.
• Migrate existing installations during the application update: generated configuration, admin customizations where supported, Sieve filters, quotas, shared folders, and the master user used by other applications.
• Keep mailbox data in place: no conversion of mail storage is expected, but indexes may be rebuilt.
• Check every integration that talks to Dovecot: Postfix SASL authentication, Rspamd spam training, Imapsync, WebTop, Roundcube, backup and restore, cloning and moving the application, and restore of a Dovecot 2.3 backup on the new version.
• Review features removed in 2.4 that we may use, and document any change of behavior in the release notes.

Alternative solutions

• Stay on Dovecot 2.3 until a new major Mail version that requires a manual migration: not acceptable, as the upgrade must be automatic for existing installations.

Additional context

SSO support for webmail clients (#8264) should be implemented after this upgrade.

Before changing defaults, PhoneHome data can tell how many installations run the Mail application and which versions.

See also

• Upgrading Dovecot 2.3 to 2.4: https://doc.dovecot.org/latest/installation/upgrade/2.3-to-2.4.html
• https://github.com/NethServer/ns8-mail