I'm wondering the following, what if shared SPF records like below are used?
v=spf1 include:_spf.google.com ~all v=spf1 include:spf.mandrillapp.com ~all v=spf1 include:servers.mcsv.net ~all
Can it affect the integrity of my domain?
Lets say I own secret.com and setup Mandrill, Google, Mailchimp or similair shared SPF records. Can my competitor bypass this security meassure by sending e-mails from competitor.com using my domain secret.com?
I assume that this way the SPF records check, will show that the domain competitor.com is allowed to send mails from my secret.com domain right? Or can the use of such shared SPF domains like above cause other risks?