In the mailgun case I received mails from for example 198.61.254.24 with from: invoice@mailgun.com
This is actually part of a bigger issue, where lots of people use the same email service to send out emails. In theory that should work with gmail or office365, but iirc gmail forces your from sometimes, and google+ms probably thought about this, right? ;)
It doesn't pass DKIM. But the fact that it's sent through Sendgrid's platform gives the e-mail credibility. Because no one expects Sendgrid to allow random customers to set e-mail (not necessarily envelope) from address to @sendgrid.com.
Not 100% sure if that was the case now, as I can't find the email anymore, but I've been getting them from both sendgrid and mailgun.
Mailgun's SPF (was at least):
In the mailgun case I received mails from for example 198.61.254.24 with from: invoice@mailgun.comThis is actually part of a bigger issue, where lots of people use the same email service to send out emails. In theory that should work with gmail or office365, but iirc gmail forces your from sometimes, and google+ms probably thought about this, right? ;)