How would UnifiedPush support work? In addition to Thunderbird supporting it, wouldn’t each account’s email server require UnifiedPush support? Assuming that’s accurate and Thunderbird supported UnifiedPush, would the benefits of UnifiedPush be negated in situations where a user has 3 email accounts configured in Thunderbird and the server of one of those accounts does not support UnifiedPush?
There is no one-size-fits-all solution and there likely isn’t a solution that works for everyone even in specific situations due to different threat models. Purchasing and using a custom domain is often listed as a good practice for maintaining a person’s privacy. However, it can be even more detrimental to a person’s privacy than just using a trusted email masking/forwarding service and trusted email provider. For example:
Please note that I am not saying that this is not a good option, but I just wanted to note some of the things that should be considered if a person decides to use a custom email domain to improve their digital privacy.