Hello @rmhhouston ,
To be honest, it actually was the likely issue for the sudden decrease. Networks and email programs regularly update their algorithms for filtering spam, based on new methods being utilized by spammers, scammers, and other malicious entities. While you might have been able to enjoy high open rates and good deliverability without self-authenticating your account for a time, simple changes to spam filters on the receiving ends can result in your email being marked as suspicious because of the lack of authentication.
The issue with this, is that we don't know when or how the algorithms have been changed, since these systems don't go around publicly announcing what exactly they changed to better filter out suspicious emails. This is why, if you're sending through our system and using a From Address with your own domain, we encourage setting up self-authentication. Without that self-auth setup, it can make it look like we're trying to spoof your address, since the email claims it's from you, but is actually originating from our servers. With self-auth setup for your account, it effectively marks as your official mailing service, and that emails from you sent through us, should be treated as though they're coming directly from your own servers.
If you have further questions regarding this, or issues getting your self-authentication setup within your account, I'd recommend contacting our delivery support team directly.
The only other element to keep in mind regarding your opens, is how opens are tracked. If the receiving programs block out the tracking pixel, or simply don't allow any images to download/display without being explicitly prompted by the recipient, then this can also affect your open rates. In Outlook, this typically presents itself as the images displaying as blank with a red X or torn page icon, until explicitly told to show the images. Apple tends to go even further, which we discuss further in our article on Apple Mail's privacy policies.
