SendGrid

SendGrid (now Twilio SendGrid) is the 800-pound gorilla of email services. They handle billions of emails monthly, and it shows in the platform's maturity. The free tier of 100 emails/day is genuinely useful for side projects.

The killer feature is having both transactional and marketing email in one place. Most competitors do one or the other. With SendGrid, you can send password resets AND run drip campaigns without integrating two services.

My gripe is deliverability. Out of the box, Postmark beats SendGrid on inbox placement. You can tune SendGrid's deliverability with dedicated IPs and domain authentication, but that's extra work and cost. For a quick setup, I'd reach for Resend or Postmark first.