A sending service is the engine that delivers your email; a campaign tool such as Cortex Mail is the dashboard you design, segment and schedule in. Here is which engine suits campaigns, which suits app emails, and how to set any of them up.
Swipe the table sideways to see every column.
| Service | Best for | Marketing campaigns | How it connects | With Cortex Mail |
|---|---|---|---|---|
| Amazon SES | High volume at the lowest cost | ✓ Yes, with production access | API or SMTP, access key | ✓ Supported: yours or ours |
| SendGrid | App emails at scale; also has campaigns | ✓ Yes | API key or SMTP | ◐ Planned |
| Brevo | Email plus SMS and WhatsApp | ✓ Yes | SMTP relay or API key | ◐ Planned |
| Mailgun | Developers who want detailed logs and routing | ✓ Yes | API key or SMTP | ◐ Planned |
| Postmark | Fast, reliable transactional email | ◐ Separate broadcast stream, strict rules | Server token or SMTP | ◐ Welcome emails, planned |
| Zoho ZeptoMail | Transactional email for Zoho users | ✕ Transactional only | SMTP or API | ◐ Welcome emails, planned |
| Mailtrap | Testing emails, then sending them | ✓ Bulk stream available | API token or SMTP | ◐ Planned |
| Gmail or Outlook mailbox | One-to-one emails | ✕ Not for bulk | SMTP with app password | ✕ Not supported, on purpose |
Based on each provider's public material as of October 2026. "Planned" means we are adding it during Cortex Mail early access; tell us which one you need.
Amazon's sending engine, used underneath many email tools. Lowest cost at volume, very reliable, and you keep full control of your domain's reputation.
Twilio's email service. Strong API and SDKs for app emails such as OTPs and receipts, with a marketing campaigns module on top.
Formerly Sendinblue. Campaigns plus SMS and WhatsApp, and an SMTP relay you can use from other tools.
A developer-focused service with detailed logs, inbound routing and email validation.
Known for fast, dependable transactional email. Broadcast (marketing) mail goes in a separate stream with strict consent rules.
Zoho's transactional email service. It does not allow promotional campaigns.
Began as a safe test inbox for developers; now sends transactional and bulk email through separate streams.
Menus differ, but every serious sending service asks for the same things.
Add your sending domain. The provider shows DNS records, usually two or three DKIM records (CNAME or TXT) and a return-path or bounce record. Add them at your DNS host and wait for the green tick.
Make sure there is one SPF record per name and a DMARC record at _dmarc.yourbrand.com. Start with p=none and tighten later. Send a test to Gmail and use Show original to confirm all three pass.
New accounts start with low daily limits. Tell the provider your expected volume and how you collect consent; ramp up over a few weeks rather than sending your whole list on day one.
Create an API key or SMTP credential that can only send. Keep the secret in the tool that uses it, never in email or chat, and replace it if it leaks.
Point the provider's webhooks or event notifications at your campaign tool so bounced and complaining addresses stop getting mail. Cortex Mail sets this up for Amazon SES automatically.
Office mailboxes allow only a few thousand recipients a day and are meant for person-to-person mail. Bulk sends get blocked and can lock the account your team depends on.
Shared hosting mail servers share IP addresses with thousands of other sites. One spammer on the same server can put your mail in spam.
Fine for one-to-one notes. For campaigns, see how it compares with a dedicated sender.
Amazon SES is usually the lowest-cost option for large volumes, at about $0.10 per 1,000 emails on Amazon's published price. Others charge more but include extras such as support, dashboards or templates.
Not at scale. Office mailboxes have daily sending limits of a few thousand recipients and are meant for person-to-person mail. Bulk sends from them get blocked and can lock the account.
ZeptoMail is for transactional email only. Postmark separates transactional and broadcast streams and is strict about consent. Use them for welcome, OTP and account emails rather than promotional campaigns.
Amazon SES first, either your own account or ours. Connecting other providers by SMTP or API is planned during early access; tell us which one you use when you request access.
