SMTP.com

If your transactional emails land in spam, the problem rarely comes from your code. It comes from the sending infrastructure and the reputation of the IP behind it. SMTP.com has been doing this job for over twenty years: you plug in their relay or their API, and your order confirmations, password resets and notifications go out from infrastructure that mailbox providers already trust.

The service advertises 99.99% uptime and is built for large volumes. From the Starter plan at 100,000 emails onward, you get a dedicated IP: your reputation belongs to you and no longer depends on what other customers send. Above that, very large senders move to custom plans with a dedicated instance, an isolated mail queue and an account manager.

• SMTP relay and API: you keep your code, you only change the sending credentials.
• Reputation Defender: an option that suppresses invalid addresses in real time before sending, to limit bounces.
• Insight Engine: an add-on that enriches your contact profiles so you can target them better.
• Assisted migration: the team handles hundreds of migrations a month from SendGrid, Mailgun and others.

The entry plan is $25/month for 50,000 emails, and support is included whatever plan you pick. SMTP.com is part of the Ziff Davis Martech division.