Sending policy
shipmail enforces sending limits at multiple levels to protect shared infrastructure, maintain high deliverability for all customers, and comply with upstream provider requirements.
Account warm-up
New accounts have gradually increasing limits to protect shared infrastructure and help you build sending reputation. The warm-up period applies per organization starting from the day the first mailbox sends an email.
| Account age | Daily limit |
|---|---|
| Day 1–3 | 50 / day |
| Day 4–7 | 200 / day |
| Day 8–14 | 500 / day |
| Day 15+ | Plan limit |
Per-mailbox rate limits
Each mailbox is limited independently, regardless of your plan quota:
- 100 unique recipients per hour per mailbox.
These limits reset on a rolling window. If you hit a limit, wait for the window to advance before retrying.
Monthly quota
Your plan determines the total number of outbound messages your organization can send per billing cycle. All mailboxes in the organization share this quota.
| Plan | Monthly quota |
|---|---|
| Solo | 1,000 / mo |
| Pro | 10,000 / mo |
| Team | 100,000 / mo |
Bounce and complaint monitoring
shipmail monitors bounce and complaint rates over a 7-day rolling window. Enforcement begins after your organization has sent at least 100 messages in the window.
| Status | Bounce rate | Complaint rate |
|---|---|---|
| Warning | 3% | 0.05% |
| Throttled | 5% | 0.1% |
| Suspended | 10% | 0.3% |
At the Warning level, your organization receives an email alert. At Throttled, sending speed is reduced. At Suspended, all outbound sending is paused until you contact support.
Suppression list
When an email bounces or a recipient files a complaint, the address is automatically added to your organization's suppression list. shipmail will reject any future send attempt to a suppressed address with a 422 recipient_suppressed error.
You can view and manage suppressed addresses through the API:
GET /api/v1/suppressionslists all suppressed addresses with the reason and timestamp.DELETE /api/v1/suppressions/{email}removes an address from the suppression list, allowing you to send to it again.
Only remove a suppression if you have confirmed the address is valid and the recipient wants to receive your email. Re-sending to an address that has bounced or complained will increase your bounce and complaint rates.
Content restrictions
shipmail scans outbound messages for patterns commonly associated with spam:
- Subject line. Subjects longer than 10 characters that are mostly uppercase are rejected. Rewrite the subject in normal sentence case.
- Link density. A single message may contain at most 20 unique URLs. Reduce the number of links or consolidate them to a single landing page.
Suspension and recovery
If your organization is suspended for exceeding bounce or complaint thresholds, all outbound sending is paused immediately. There is no automatic recovery. Contact support@shipmail.to with the steps you have taken to fix the underlying issue. Sending is re-enabled after review.
Best practices
- Clean your list. Remove addresses that have bounced. Check your suppression list regularly.
- Authenticate your domain. Verify SPF, DKIM, and DMARC records in the dashboard before sending.
- Warm up gradually. Respect the warm-up schedule. Do not attempt to send your full volume on day one.
- Monitor your analytics. Watch bounce and complaint rates in the dashboard and set up webhooks for real-time notifications.