Providers

Free tiers

• Postmark: 100 free per month no CC
• Sendgrid: 100 free per day no CC
• SMTP2GO: 1000 free per month no CC

Not sure if this still works:

• Mailgun: 1000 free per month with CC
• TransIP: has free outgoing mail with a VPS

Interesting:

• MailerSend link