To allow Extravision to send emails on your behalf, you will have to add them to your SPF record. The SPF mechanism used by Extravision is shown below.
You can configure DKIM support through Extravision's technology partner Port25 via the configuration tool they have on their website as follows:
Visit the Port25 DKIM wizard website here
Enter your domain name in the box provided. For example, if your sub-domain is mail.mycompany.com then enter "mail.mycompany.com"
The domain key selector is used to specify which key is to be used to sign an outgoing email. This can be anything so the example of key1 is fine
Keep the default key size of 1024 bits
Select "Create Keys"
The instructions on the next page tell you which DNS records you need to create for DKIM. There are 2 TXT records that you need to create, the Selector record and the Policy record.
Steps 2 & 3 are for Extravision to implement. Please save a copy of the page and email it to domainkeys @ extravision.com. Extravision will reply and let you know as soon as your DKIM key has been setup and verified.
Create a free OnDMARC account to test your configuration.