You should check to see if the messages that are being sent contain any links that would be considered questionable/spammy. You can also try taking the content of one of the messages and checking it’s spam assassin score ( https://spamcheck.postmarkapp.com ). Source: over 2 years ago

Build a clean email that passes a spam check with flying colors (https://spamcheck.postmarkapp.com/) then use a warmup service like lemwarm, inboxally or neverspam as mentioned in the other comments. Source: almost 3 years ago

The issue sounds more email centric. You're likely hitting the Apache SpamAssassin limit on the remote email servers. Use https://spamcheck.postmarkapp.com/ to check the score of emails you've had declared spam, and follow recommendations to improve. Source: almost 3 years ago

Ugly Email claims to block tracking pixels from 58 domains. The Firefox addon was last updated in 2020, and the Github in 2022. Source: 12 months ago

There have been some attempts by Google to restrict the amount of information that can be transmitted this way. For example,since 2013, Google has served all images in Gmail through its own proxy servers, which could hide your location from at least some tracking applications. And extensions such as Ugly Email and Pixel Block have been developed to block trackers on Chrome and Firefox. Source: over 2 years ago

Implementing something like ugly email would be ideal, not just blocking remote content from auto loading. Source: almost 3 years ago

Disabling automatic image loading in your mail client settings or using extensions like Ugly Email can help preventing this. Source: about 3 years ago