Reference
Limits and windows
Every limit and time window in one table, from 50 recipients per message to 100 API requests per minute.
Tested with resend@6.30.0
Last reviewed
On this page (2)
| What | Limit | More |
|---|---|---|
| Sending | ||
| Recipients per message | 50 | Sending |
| Attachments per message | 20 | Attachments |
| Attachments per request, decoded | about 10 MB | Attachments |
| Text and html | 250,000 characters each | Parameters |
| Messages per batch | 100 | Batch |
| Scheduling ahead | 30 days | Scheduling |
| Idempotency keys | 24 hours | Idempotency |
| API | ||
| API requests | 100 per minute per project and environment | Rate limit |
| Domain additions | 5 per minute per project | Domains |
| Domain verifications | 10 per minute per project | Domains |
| Webhooks and receiving | ||
| Webhook attempts | 8 over about 27½ hours | Retries |
| Webhook response window | 5 seconds per attempt | Retries |
| Received message size | About 14 MB, attachments included | Receiving |
| Download links | 15 minutes | Attachments |
| Received-mail list | Latest 100 | Listing |
| Retention | ||
| Messages, attachments and events | 1–90 days (default 30) | Retention |
| Postal’s own copies | Raw mail 7 days, metadata 30 days | Retention |
| Backups | 7 daily recovery points; one copy from 29 September 2026 doesn’t expire automatically | Retention |
| Dashboard sign-in | ||
| Sign-in codes | 10 minutes, 5 attempts | Security |
| Sessions | 7 days | Security |
| Code requests | 6 per address per hour | |
| New code | At most one every 60 seconds per address | |
| Code checks | 20 per address per 15 minutes | |
| Mail server | ||
| Initial Postal limit | 1,000 messages per hour per project, an abuse guard, not a delivery target | Below |
Limits and windows. Not performance claims.
Sending
- Recipients per message
- Limit
- 50
- More
- Sending
- Attachments per message
- Limit
- 20
- More
- Attachments
- Attachments per request, decoded
- Limit
- about 10 MB
- More
- Attachments
- Text and html
- Limit
- 250,000 characters each
- More
- Parameters
- Messages per batch
- Limit
- 100
- More
- Batch
- Scheduling ahead
- Limit
- 30 days
- More
- Scheduling
- Idempotency keys
- Limit
- 24 hours
- More
- Idempotency
API
- API requests
- Limit
- 100 per minute per project and environment
- More
- Rate limit
- Domain additions
- Limit
- 5 per minute per project
- More
- Domains
- Domain verifications
- Limit
- 10 per minute per project
- More
- Domains
Webhooks and receiving
- Webhook attempts
- Limit
- 8 over about 27½ hours
- More
- Retries
- Webhook response window
- Limit
- 5 seconds per attempt
- More
- Retries
- Received message size
- Limit
- About 14 MB, attachments included
- More
- Receiving
- Download links
- Limit
- 15 minutes
- More
- Attachments
- Received-mail list
- Limit
- Latest 100
- More
- Listing
Retention
Dashboard sign-in
Mail server
- Initial Postal limit
- Limit
- 1,000 messages per hour per project, an abuse guard, not a delivery target
- More
- Below
These are limits and time windows, not performance claims. The initial Postal limit of 1,000 messages per hour per project guards against abuse; it isn’t a delivery target, and Letterpier makes no promises about throughput or delivery times.
Retention applies to the copies Letterpier keeps. Backups expire on their own schedule, except the copy of 29 September 2026 described under retention, and mail you delivered stays in the recipient’s mailbox.