Squashed commit of the following: SPF fixes #6537 !1765

commit 8fe6d116
Author: Herman van Rink <rink@initfour.nl>
Date:   Sun Jul 23 17:26:39 2023 +0200

    Rewrite to improve readability

commit dfdab8a1
Author: Herman van Rink <rink@initfour.nl>
Date:   Tue Jul 4 21:55:12 2023 +0200

    Better detect an existing spf record, #6537

    '' and 'example.com.' are effectively the same.

commit 713b6221
Author: Herman van Rink <rink@initfour.nl>
Date:   Tue Jul 4 21:54:47 2023 +0200

    Initialize new SPF record to have a hostname, #6537