What is dkim.mcsv.net?
dkim.mscv.net is a hostname used as part of Mailchimps email domain authentication. For the most part it is not something you should see or use unless you're authorizing Mailchimp to deliver emails from your domain.
Email domain authentication on Mailchimp
In order to authenticate your domain on Mailchimp, you need to a DNS CNAME record on your domain that tells email servers that Mailchimp is allowed to send emails on your behalf.
If you don't configure this you risk your email being flagged as violating DMARC and not reach its recipient.
Mailchimp potentially instructs you to create CNAME records for the following hostnames:
Our guide to setting up DKIM for your domain uses Mailchimp as an example.