Microsoft shared an Office 365 Free DMARC solution a few days ago, with a partnership with ValiMail. You can subscribe to the service on this link.
You can read the complete announcement there.
I found it to be an excellent news to be able to get some DMARC insights free of charges, so I tried it, hereunder my firsts impressions.
Subscribe
First, you need to subscribe to the service on ValiMail’s site.

Then, you’ll receive an email with the instructions (it took ~2 days for me, maybe caused by a huge load since the announcement).
Basically, you’ll need to create a “_dmarc” subdomain in your DNS registrar, and then add their name server to let ValiMail handle DMARC configuration for you.
Note: You may want your security team to review this before implementing into production.
Once the new DNS record is detected by ValiMail, they will send you your credentials to access your ValiMail dashboard to access your statistics.
Usage
If you have a look at your DMARC, you’ll see something like this:

Valimail will manage this for you, you won’t have to learn the DMARC DNS specifications.
As soon as you accept the invitation to access your Valimail dashboard, you’ll be asked to create a password for your account, and then you’ll be able to see the DMARC reports.
Based on the harvested data, Valimail will allow you to deploy SPF/DKIM records that matches your deployment.