Are you looking for personal e-mail, transactional e-mail or a service for newsletters and such?

For personal e-mail you could try either one of Zoho Mail, Outlook, Gmail or iCloud Mail.

For transactional e-mail you could try SendGrid, Mailgun or Amazon SES. All of them have free tiers. I've been using Sendgrid for a while and could recommend them.

When sending out newsletters you could use Mailchimp or SendGrid, both also offering free tiers.