TL;DR. I ended up using Smtp2Go

My website uses minimal email traffic, but it does send emails from time to time: mostly to myself as notifications.

I could probably get by with GMail for this kind of usage, but I wanted to avoid any limitations, to I was using SendGrid free plan.
Unfortunately, it has been discontinued. I asked ChatGPT for advice, and it recommended MailerSend, SMTP2Go, Brevo, Mailgun and Postmark.

I started with MailerSend, and it did not go very well. Firstly, they wanted to me to authorize my entire domain, meaning creating a bunch of DNS records to prove I own it. They don’t allow creating individual authorized senders, this is a paid feature. Second, they asked me to describe my project and its “business model” and wanted to see invoices from my previous provider. My project is not for profit, so I did not have much to say about business model or invoices. As a result, it was not approved, meaning I would not be able to use MailerSend beyond the first 100 trial emails. I did not get to actually sending emails through them.

I moved to SMTP2Go. With them, you can validate a domain, or you can validate an individual sender by simply entering an email address and clicking on a link once you received a verification email. Setting up SMTP was straightforward: I was up and running in about 30 minutes. I use msmtp internally, so I just added a new configuration instead of SendGrid’s and voila.

I believe I get 1000 emails per month, and that’s more than enough for my modest purposes.

I did not try Brevo. Allegedly they allow 300 emails per day, but I don’t need that many.