What email API should I use at 100k emails a month?

At 100k emails/month, you’re at a volume where you should use a dedicated email delivery API, not a general SMTP inbox provider.

Good options

• SendGrid — very common, easy API, good deliverability tooling
• Amazon SES — cheapest at scale, very solid, more “infrastructure-y”
• Postmark — excellent deliverability and simplicity, usually best for transactional email
• Mailgun — flexible, good APIs/logging, often used for app email
• Resend — modern developer experience, good for product emails/startups

My practical recommendation

• If you want lowest cost: Amazon SES
• If you want best developer experience / fast setup: Resend or SendGrid
• If this is transactional email and reliability matters most: Postmark
• If you want a balanced default choice: SendGrid

A quick rule of thumb

• Transactional emails (password resets, receipts, alerts): Postmark / SES / SendGrid
• Marketing emails: SendGrid / Mailgun / Mailchimp / Klaviyo depending on campaign needs

Things to check before choosing

• Deliverability reputation
• DKIM/SPF/DMARC support
• Webhooks for bounces/complaints
• Dedicated IP availability if needed
• Pricing at 100k/month
• Ease of template management
• Suppression lists and unsubscribe handling

If you want one answer

If you’re sending 100k emails/month, I’d usually pick:

• Postmark for transactional email
• Amazon SES if cost is the priority
• SendGrid if you want the most mainstream all-around option

If you tell me whether these are transactional or marketing emails, and whether you care more about cost, deliverability, or ease of use, I can narrow it to one best choice.