What email service is best for building personal brand?

I've been using Fastmail and I'm very happy with their service. It's affordable, the calendar is great and you have ton of control when using your own domain.

I'm a little unsure if I understand what you're asking for since you talk about personal branding and it makes me wonder if you're looking for an email sending/newsletter service rather than just an email hosting service.

For email hosting service, I don't think there are any email services specifically tailored or extra relevant to building personal brands. Things like a proclaimed security focus and ability to use your own domain are common features among many services. Fastmail, ProtonMail, Zoho Mail, etc.

If you actually mean you're looking for an email marketing/newsletter sending service, I personally use and have been happy with Mailerlite. It has reasonable price points (with a free tier), automation, lets you use your own domain, and lets you section subscribers into different tags easily. Deliverability is improved if you use your own domain rather than a generic free email (which Mailerlite does not recommend).

I have been using Fastmail for many years and do recommend them. They do provide a 30 day trial period that may be useful?

Do you have iCloud+? It allows custom domains now.

Protonmail

Office365