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Premium Relay

Multi-relay system for high deliverability

Features

  • Carefully vetted and run-in IPs with excellent reputation.
  • Ensure near 100% deliverability to all major providers and ESPs through Mailcheap's multi-relay system which resends hard rejects.
  • Powerful anti-spam and anti-virus outbound filtering to maintain IP reputation.
  • Provided as standard with all our hosted email products/plans.

Restrictions

  • Transmitting bulk emails or commercial emails including marketing emails and newsletters.
  • There is no single upper limit for sending but instead a per-user and recipients per-IP limit.

Sending limits

Rate limits are based on leaky bucket algorithm and has separate limits for local mail (same domain including subdomains) and external mail.

Leaky bucket is very easy to visualize, consider it as a bucket that has a certain capacity with a hole at the bottom through which its contents are leaked over time. In our case, the bucket holds emails and leaks emails from the hole at the bottom. The important parameters of this leaky bucket are its capacity and leak rate.

It is important to note that the leaky bucket does not delay messages, it simply counts them. Amending our previous statement, the bucket holds emails email count and leaks emails the count from the hole at the bottom. A bucket would only reach capacity if the sending rate exceeds the leak rate.

The system would issue a soft reject if over quota (on reaching bucket capacity), so any mails in queue would be accepted for delivery later. The leaky bucket does not delay messages that are accepted, even when reaching capacity, it only soft rejects the mail so that the client can automatically retry after some time.

Per-user buckets & their properties
  • Local mail → Capacity: 200 | Leak rate: 1 message every minute
  • External mail → Capacity: 50 | Leak rate: 1 message every 3.6 minutes
Recipients per-IP bucket & its properties
  • Recipients per sender-IP → Capacity: 500 | Leak rate: 1 message every minute

Each message can have up to a maximum of 50 recipients, please note that each recipient is counted as a single message towards quota calculation. That is, 50 messages to 1 recipient each are counted as 50 messages, while 1 message to 50 recipients is also counted as 50 messages.

Sending without limits

To send without rate-limiting on Cloud/Dedicated mailservers, Premium relay can be turned off (may affect deliverability) by contacting support. Cloud/Dedicated mailservers can be configured to use any external SMTP relay service of your choice. Please note that two-factor authentication (2FA) is mandatory for MailUser accounts (email accounts) if Premium relay is disabled and there is no external relayhost/smarthost configured. This is to prevent compromised user spamming incidents as there are no sending limits without Premium relay. The system disables a MailUser if 2FA is disabled for 3 consecutive days.