You can access your DNS settings by clicking on Domain and DNS > Manage Zones as explained here :

Step 1.

You need to configure the domain name from which your newsletter will be sent. Head to Jackmail plugin’s settings and enter the subdomain you want to us (our example here : news.jackmail.com)

Step 2.

When you hit ‘Next’, Jackmail will assign a TXT key for this domain. You’ll have to enter this TXT value in your Dreamhost panel.

Head to Go Daddy and add the TXT record by clicking on ADD

Add the TXT record shown in Jackmail plugin wizard, and don’t forget characters, like “==”

Step 3.

Head back to Jackmail and hit next. You’ll have now NS records to add. Be careful, it’s now on the subdomain!

NS records are the same for everyone. You don’t have to customize them. Just copy and paste the whole record

• dns.customizedurl.com.
• dns2.customizedurl.com.

Watch out for the last . after com, it’s mandatory

In your Go Daddy panel,  add now two more records of type Nameserver and specify `news.jackmail.com` in the Host field. Type the values provided by Jackmail in ‘Points to’.
Do this step twice, once for each of the NS records required.

Once these steps are done, hit Save on Jackmail plugin and try sending your first email.
Remember that changes in DNS zones can take between 24 and 48 hours to take effect.