Resource limits

Resource Limits

To keep the service reliable and protect the sending reputation shared by all customers, a number of limits apply to how you send transactional e-mail messages and how many resources you can create. Most limits are generous defaults that suit typical transactional use; where a limit can be raised, the documentation says so and how to request a change.

Message limits

• Recipients per message: You may address a message to 1024 recipients across To, CC, and BCC combined. Note that very large recipient lists on a single message can slow delivery and are better split into separate messages; the sending quota below still applies to the total.
• Maximum message size: 5 MB. This is the size of the complete message as transmitted — headers, body, and attachments. Because attachments are MIME encoded for transport (which adds roughly one third to their raw size), the practical budget for original attachment content is about 3.7 MB.
• Messages per connection: You can send up to 10,000 messages over a single authenticated SMTP connection before it must be closed and reopened. Reusing one connection for many messages — rather than reconnecting for each message — is more efficient and is the recommended pattern.

Sending quota

• Default sending quota: 10 messages per hour, per sending domain. New sending domains start with this conservative quota so that sending reputation can be established gradually. Need to send more? Open a service request with the support team to raise the quota for a sending domain.
• Concurrent SMTP connections: up to 50 per account. This is the number of simultaneous authenticated SMTP connections you may hold open at once. Additional connection attempts beyond this limit are refused until an existing connection is closed. Reuse connections for multiple messages rather than opening a new one per message.

Object resource limits

• You can create up to 100 Sending Domains per project.
• You can create up to 50 Authorized Senders per Sending Domain.