I was looking into SendGrid and came upon this interesting forum post saying you don't have to make DNS mods to ensure deliverability: http://community.sendgrid.com/sendgrid/topics/why_dont_i_need_an_spf_record_or_other_dns_mods
Our Free accounts do not require any DNS changes because we set the return path header, SPF, and DomainKeys headers to point to SendGrid's SPF and DomainKeys.
My question is if this approach is reliable and the experience from our clients' side isn't affected. Also, what's stopping anyone from sending emails on behalf of our domain if SendGrid automatically makes them seem reliable?
Thanks, Vilem