I asked them about it and they never replied. I wish it was just a native (or not) IMAP client and I definitely want out of those Link and Open Tracking features.
(Edit):
There's a GitHub issue related to it - https://github.com/Foundry376/Mailspring/issues/33
The dev is very clear about it
--- but for now Mailspring needs to target paying customers with great pro features so I can continue working on it full-time. The Mailspring ID is a core component of these Pro features and a lot of exciting stuff on the roadmap, like team templates, read receipt analytics and shared folders. Unfortunately, it doesn't make sense to remove the Mailspring ID and make the mail client better for you, because it pulls us further away from doing a great job on the pro features for paying users that will ultimately make this a long-lasting open source project.
Hope that helps! I'm going to flag this as a wontfix for now, but I welcome everyone's thoughts and feedback here. ---
So no, not an email client I would like to use.