So even sending that domain won't be sufficient in whitelisting our communications? (Or at least, a customer would be less likely?) |
It wouldn't whitelist only your communications. So while you could feign ignorance and say that it only applies to your instance, it would eventually be clear that it doesn't.
The only factor that applies to your instance exclusively is the DKIM signature on the message. If you can get someone to whitelist based on DKIM PASS for selector "M1" those emails are guaranteed to be from you, and only from you.
Another thing to consider is if somebody is blacklisting Marketo IPs outright, they likely won't get to the point of being able to whitelist based on other, more granular, info. That is, they might have been OK with your email if they got to see the MAIL FROM SMTP command, but in technical terms MAIL FROM comes after the initial connection and HELO/EHLO SMTP command.
I know this may seem overly technical, but the SMTP protocol is actually really simple, following this sequence (from the sender side) if things are good:
- recipient's server says, "Hello, who are you?"
- sender says, "I am outbound-123.mktomail.com"
- recipient says, "That sounds good, keep talking"
- sender says, "I have an email from 123-456.01.02.04@em-sj-77.mktomail.com"
- recipient says, "Yeah, who's it going to?"
If things are bad, the recipient can say "Goodbye" at any point, including at the very beginning (since it knows the sender's IP address) or after seeing "outbound-123.mktomail.com" and identifying Marketo that way. Thus it might not get to the point of going, "Ohhhh, you're from Marketo, but you're on our special list."
Similarly, even though whitelisting based on DKIM would be awesome and secure, they won't see the DKIM signature until the message has been transmitted (which is a few steps later in the sequence above).
.png)