I’m quite paranoid and put a lot of effort into maintaining a good security posture. Rather than worrying about the security of my emails, however, I simply ass

I’m quite paranoid and put a lot of effort into maintaining a good security posture. Rather than worrying about the security of my emails, however, I simply assume that any email I send or receive may become public one day. Remember, there is always a third party on the other end of the email, and you cannot control what they do with their copy of it. You can have the most secure email server in the world, but unless you’re sending emails to yourself, that security goes out the window once another correspondent is involved. Consider this: every time you send an email to someone with a @gmail.com address, there is a copy of your email stored on google servers (not to mention it might even get spam filtered). So did you do all that work to secure your email for nothing? The one exception is for security related, primarily inbound, emails (password resets, OTP codes, etc.). Here I can see the argument for self hosting. Ideally you would keep a separate email for all signups / transactional emails that is used 99% for inbound, and isolated from any of your public email addresses.