Documentation

With archiveMode enabled, all sent mails are kept in the queue table, including their content, until the sent retention removes them.

That answers the classic support question—"was the license mail actually sent, and with which content?"—and it enables re-sending any mail from the backend module with one click.

The setting is also available under Settings → Extension Configuration → mail_queue.

The archive contains personal data and full mail contents. Three things follow, and none of them is optional:

• Keep sentRetentionDays deliberately short. The default is 30 days, which is already generous for an archive that holds password reset mails.
• Grant the module only to trusted users. See Access Levels for how to delegate it without handing out the destructive controls.
• Mention the retention in the instance’s privacy documentation.

Archive mode changes what "sent" costs you. Without it, a delivered mail's payload is dropped immediately. With it, every sent mail keeps its content until sentRetentionDays expires—in the table, and for mails with attachments also as a file in var/mailqueue/. Archive mode is therefore the one setting that makes a successful delivery consume disk.

On an instance that sends a lot of mail, check the size of tx_mailqueue_message and of var/mailqueue/ after the first retention cycle and adjust from there.