Sending rate limits¶
Kopano Cloud uses a leaky bucket rate limiter for outbound mail. Each quota is fully restored at the start of every 12-hour interval; there is no gradual refill.
Quotas¶
| Scope | Messages per 12 hours |
|---|---|
| Mailbox | 500 |
| Organisation | 1,000 |
| Domain | 1,000 |
| Internal | 1,000 |
Scope definitions¶
- Mailbox — per-mailbox limit. Applies to every sending mailbox individually.
- Organisation — aggregate across all mailboxes in the organisation. Reaching this ceiling blocks further outbound mail from any mailbox in the account until the interval resets.
- Domain — aggregate for messages sent by mailboxes sharing the same sender domain. Sending more than 1,000 messages from
@example.comwithin one interval triggers this limit regardless of how many mailboxes sent them. - Internal — messages between mailboxes on the same Kopano Cloud instance. Internal traffic is tracked separately and does not consume the outbound quota.
Warning
Messages that exceed a rate limit are rejected. The sender receives a bounce notification in their mailbox.
Tip
For bulk sends (newsletters, notifications), stay within per-mailbox quotas. Distributing sends across multiple mailboxes reduces per-mailbox pressure but the organisation and domain limits still apply in aggregate.