Hello @Jim.Schratz ,
I spoke with a member of the review/deliverability team, and they pointed out that "Earthlink has a very strict rate limiting procedure they use." Essentially what this means is Earthlink is an ISP that limits (throttles) the amount of emails they accept from a particular sender during a specified period of time. If you try to send email above their acceptable threshold, they will reject your email - resulting in a high number of bouncebacks. This is email throttling and is also referred to as a “deferral.”
This refusal to deliver your mail is usually temporary, but it depends on the situation. When your emails are throttled, you will get a message that says something like “user is receiving mail at too great a rate right now, please try again later,” or “user’s mailbox is over quota." Ultimately, it has nothing to do with our system's ability to send and deliver to Earthlink. It's an issue of their system processing too many emails and just cutting off delivery in general. This can be particularly potent during busier email periods, such as election seasons or major holidays.
If you're wanting the logs for these bounces, to learn more about Earthlink's deferrals / throttling, or for advice about best sending times for Earthlink addresses, I'd suggest reaching out to our Review / Deliverability team.