Add DMARC records for openfoodfacts.org mails

[alexgarel]

Describe the bug

DMARC is not ok for adresses of openfoodfacts.org

 You do not have a DMARC record
A DMARC policy allows a sender to indicate that their emails are protected by SPF and/or DKIM, and give instruction if neither of those authentication methods passes. Please be sure you have a DKIM and SPF set before using DMARC.

You do not have a DMARC record, please add a TXT record to your domain _dmarc.openfoodfacts.org with the following value:

v=DMARC1; p=none

Verification details:

    mail-tester.com; dmarc=none header.from=openfoodfacts.org
    mail-tester.com; dkim=pass (2048-bit key; unprotected) header.d=openfoodfacts-org.20210112.gappssmtp.com header.i=@openfoodfacts-org.20210112.gappssmtp.com header.b=UPcuy/aE; dkim-atps=neutral
    From Domain: openfoodfacts.org
    DKIM Domain: openfoodfacts-org.20210112.gappssmtp.com

To Reproduce

You can use https://www.mail-tester.com

[alexgarel]

Maybe it's more general, for example I can't try a mail sent from the server.

So:

• do we add good spf record (with all server adress sending emails) and it is documented to add new servers that send emails to spf
• is the DKIM certificate deployed on all servers, and then again documented
• is the DMARC right ?