How to include multiple spf domains with different mechanisms in a single spf TXT Record [duplicate]
You can combine them all like this.
v=spf1 a mx ptr ip4:x.x.x.x ip4:y.y.y.y include:mktomail.com include:icpbounce.com include:spf.mandrillapp.com -all
I recommend changing the ~all to -all - the whole point in setting up authentication in the first place is to make it fail when it's violated. Then test sending emails from all the different places to a testing tool like [email protected]. To ensure the SPF passes from each send point.