How can I update SPF when a record already exists?
In some cases you might already have an SPF record for your domain. For example, SPF is recommended when using Google Apps or an email marketing service. If this is the case, updating your existing record is simple.
Let’s say your current records looks like this:
v=spf1 a mx include:_spf.google.com ~all
In this case, you just update your record to include Postmark:
v=spf1 a mx include:spf.mtasv.net include:_spf.google.com ~all