Re: dmarc?
DMARC is a tricky beast. If you enforce it then say goodbye to mailing lists for starters. See Yahoo for what happens when you publish a "please enforce my DMARC policy".
Now, you should run your DMARC in monitor mode for a fair old while before requesting enforcement. You can request daily digests or even forensics level diags from other mail systems and many will send them. You evaluate the side effects and then you set enforce.
_dmarc.ntlworld.com. 899 IN TXT "v=DMARC1; p=none; rua=mailto:root.mail@virginmedia.co.uk"
They haven't done the whole thing yet. Note: p=none