Enh: option to use timestamp from headers if there is no Date: header

[sebbASF]

Some messages don't have a Date: header.

The importer generally runs a long while after the messages were sent, so using the current time causes problems.

It would be useful to have an option for the importer to use another date, for example the From_ line normally has a timestamp. There are also timestamps in the Received: lines. The last one will normally be closest to the creation date of the mail.

The archiver may also benefit from the option. The mail will normally be received by the archiver soon after it is sent. But if there are multiple archivers, their timestamps may vary.