MailerSend vs Twilio SendGrid

MailerSend

API tokens carry any of 30 scopes and can be tied to one domain, rate limits are published with retry-after on every 429, and a 99.5 per cent SLA starts on the $35 Starter plan. Sends take no idempotency key, the Free plan allows 100 API requests a day, and the terms permit changes without notice.

Twilio SendGrid

Restricted API keys with per-endpoint scopes, subuser keys and IP access management. No official MCP server that can send, only Twilio's docs search.

MailerSend

1. Send Authorization: Bearer <token> to https://api.mailersend.com/v1 and ask for a token with only the scopes the task needs, such as email_full and activity_read
2. Read the message id from the x-message-id response header. POST /v1/email answers 202 with an empty body
3. Check for a sent message before retrying a send. No idempotency key exists, so a blind retry can deliver twice
4. On a 429 wait the seconds in retry-after. Call GET /v1/api-quota, which isn't counted, to see the daily quota left
5. Use POST /v1/bulk-email for batches of up to 500 emails. It isn't on the Free plan and takes 10 to 60 requests a minute by plan

Twilio SendGrid

1. Give an agent that only sends a restricted key with just mail.send
2. Set mail_settings.sandbox_mode to validate payloads without delivery
3. Authenticate a domain or verify a single sender before the first send
4. Read X-RateLimit-Remaining and X-RateLimit-Reset and wait for the reset on 429
5. Don't blindly retry a timed-out mail/send. There's no idempotency key, so the message can go out twice