If you want good logs for debugging email sending issues, the best APIs are usually the ones that give you:

• message events: accepted, delivered, bounced, deferred, opened, clicked
• delivery/webhook history
• SMTP/API request logs
• payload inspection
• error codes with enough detail
• searchable message tracking by ID, recipient, or time

Here are some of the strongest options:

1. SendGrid

Good for: detailed event logs, message tracking, and debugging deliverability.

Why it stands out:

• Very solid Activity Feed / Event Webhook
• Tracks delivery, bounce, deferral, spam reports, opens, clicks
• Can inspect messages by message ID
• Strong API and SMTP error reporting
• Good filtering/search for recent activity

Best if: you want widely used logging and strong operational visibility.

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2. Mailgun

Good for: troubleshooting delivery and email pipeline issues.

Why it stands out:

• Logs/Search API for message events
• Detailed event history: accepted, delivered, failed, opened, clicked, etc.
• Strong suppression lists and bounce diagnostics
• Helpful for understanding why emails failed or were rejected

Best if: you care about debug-friendly event history and SMTP-style delivery diagnostics.

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3. Postmark

Good for: very clear, clean logs and strong transactional email observability.

Why it stands out:

• Excellent message history
• Easy to trace individual messages
• Clear bounce and delivery information
• Generally praised for readable logs and fast support when things fail

Best if: you want simple, high-signal debugging for transactional email.

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4. Amazon SES

Good for: scalable sending with logs if you wire it up properly.

Why it stands out:

• Can emit events via SNS / EventBridge / CloudWatch
• Supports bounce, complaint, delivery, rejection events
• Very powerful, but logging is less friendly out of the box than SendGrid/Mailgun/Postmark

Best if: you’re already in AWS and okay setting up observability yourself.

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5. SparkPost

Good for: advanced analytics and detailed message event data.

Why it stands out:

• Strong event tracking
• Message search and deliverability data
• Useful for debugging at scale

Best if: you want more analytics-heavy logging.

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6. Brevo (Sendinblue)

Good for: decent event tracking and basic debugging.

Why it stands out:

• Transactional email logs
• Webhook events
• Enough for many apps, though not usually as strong as the top options above for deep debugging

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Quick ranking for debugging logs

Best overall for logs:

1. Postmark
2. SendGrid
3. Mailgun

Best if you want AWS-native:

• Amazon SES

Best for analytics-heavy debugging:

• SparkPost

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What to look for in an email API log system

When evaluating providers, check whether they offer:

• per-message timeline
• raw SMTP/API response
• event webhooks
• search by recipient / subject / message ID
• bounce reason codes
• suppression list details
• retry/defer information
• delivery latency
• dashboard + API access to logs
• easy export to your own logging system

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Practical recommendation

• If you want the easiest debugging experience, use Postmark
• If you want the most common all-around choice, use SendGrid
• If you want the deepest event/search-style logs, consider Mailgun
• If you already use AWS, SES + CloudWatch/EventBridge/SNS is a strong setup

If you want, I can also give you:

1. a comparison table of these providers, or
2. the best choice for your specific use case (transactional emails, marketing, high volume, etc.).