Limits & Quotas
Overview of API rate limits, request payload limits, and daily Gmail quotas.
The following limits apply to accounts to ensure platform stability and protect fair usage. Pro plan upgrades increase these limits significantly.
API Rate Limits
| Endpoint | Limit | Window | Keyed By |
|---|---|---|---|
POST /api/send | 60 requests (300 on Pro) | per minute | API key |
GET /api/auth/* | 10 requests | per minute | IP address |
When a rate limit is hit, the API returns 429 Too Many Requests with a Retry-After header indicating how many seconds to wait.
Request Payload Limits
| Field | Limit | Notes |
|---|---|---|
subject | 998 characters | RFC 2822 maximum |
html | 2 MB (5 MB on Pro) | UTF-8 encoded |
text | 1 MB (2 MB on Pro) | UTF-8 encoded |
to / cc / bcc | 50 recipients each | String or array of strings |
attachments | 10 files · 25 MB total (20 files · 25 MB total on Pro) | Base64-encoded content. Max 10MB per file. 25MB total is Gmail API's hard limit. |
Account & Daily Limits
| Resource | Limit | Notes |
|---|---|---|
| Connected Gmail Accounts | 10 accounts max (50 max on Pro) | Per SendLib user account |
| Active API Keys | 15 keys max (100 max on Pro) | Per SendLib user account |
Personal Gmail (@gmail.com) | 500 emails / day | Resets daily at UTC midnight (enforced by Google) |
| Google Workspace Account | 2,000 emails / day | Resets daily at UTC midnight (enforced by Google) |
Daily sending quotas are set and enforced directly by Google's Gmail API. SendLib monitors your send volume and resets your limit tracking daily at UTC midnight.