I have successfully added the Campaign Monitor SSPF code to a DNS TXT record in the past...
v=spf1 mx include:cmail1.com ~all
I now have a situation where I need to set this up for another domain, but that domain already has an SPF TXT record set up. For example:
v=spf1 mx include:service.anotherdomain.com ~all
How do I set up the Campaign Monitor TXT record while retaining the existing SPF records as emails are going to continue to be send by the other service as well as Campaign Monitor?
Yup, that's easily doable. You just have to add another "include" so the correct record would be something like this:
v=spf1 mx include:cmail1.com include:service.anotherdomain.com ~all
Hope that helps!