Hello
I performed lookups for both link.potomacco.com and links.potomacco.com, and neither seems to be externally resolvable. As such, your links would be invalid when branded with either of these CNAMEs. You will want to make sure that links.potomacco.com is set up correctly in your DNS host, and if your organization is using both internal and external DNS, set up the CNAME value in both.
That being said, social links are not branded with the CNAME value you set in DNS Settings, they are branded with the subdomain alias CNAME value that you set up on the domain record for your domain (found in settings > Domains in CRM). This value also needs to be set up in your DNS host. If you have multiple domain records and subdomain alias values set up in your CRM, there should be a drop down list in the social links settings area in your email template editor that will let you pick which value is used to brand the social links.
The following article discusses how to set up CNAMEs and subdomain alias: http://help.clickdimensions.com/setup-cnames/
and this articles discusses social links and shows where you pick the domain value to use with them in different email editors: http://blog.clickdimensions.com/2014/04/adding-social-sharing-links-to-your-emails-in-the-drag-and-drop-designer-1.html
http://help.clickdimensions.com/how-to-insert-social-links-into-an-email-template/