To protect the hosted email service and ensure a timely and reliable experience for customers, we maintain reasonable limits for the number of email messages that users can send and receive. All limits are rate-based, meaning a certain number of messages or recipients are allowed in a certain timeframe. If the limits are exceeded, continued attempts will either be deferred or rejected by the hosted email platform. These limits are applied to both incoming (receiving) and outgoing (sending) email.
Automated email and spam are restricted at much lower limits to protect the integrity of the system. We reserve the right to change any limits without warning or notice to ensure the integrity of the email service.
To limit the ability of bad actors from using our service to send spoofing emails, we will begin enforcing additional verification on all emails sent from our system, to limit the available sending domains to ones on the same account as the authenticated user. The limitation of sender domains to your account dramatically reduces the ability of bad actors to send phishing/spoofing emails from the hosted email service, in ways that traditional DNS-based checks cannot, when using a multi-tenant hosted email service.
Specifically, the two addresses used for this verification are: the authenticated user’s address, and the sender address in the SMTP MAIL FROM address. If the domains of these two addresses are on the same customer account, then the verification passes. Otherwise, it fails, and the message will be rejected.
To accommodate the need to use sending-only domains or sub-domains, a domain alias can be added to an existing primary domain, on your customer account. The sender domain check will pass for both primary domains and domain aliases.
Daily limits apply to a 24-hour calendar day (00:00:00 until 23:59:59) and restrict the total number of recipients to which a user can send messages in this period.
Users are limited to 10,000 total recipients per 24-hour period. Counting recipients is different than counting messages. For example, sending 100 emails that each have 100 recipients is counted the same as sending 10,000 emails that each have a single recipient.
The mail platform limits the rate at which a mailbox can receive messages. The purpose of the receiving limit is to control the rate at which a user is receiving mail. This helps to ensure a positive user experience when accessing, reading, and sending email. It also protects all users from a degraded experience due to a small number of users utilizing the majority of resources.
If a mailbox receives over 400 messages in a 10-minute period, any additional messages in that period will be deferred. Email senders will typically retry a deferred message at least once, possibly resulting in the message still being delivered after a short delay.
Mailboxes designated to receive high-volume automated email have an increased potential of being impacted by this limit. For example, mailboxes set to receive from devices or programs that send diagnostic information via email, and systems which generate high volumes of email from services like CRMs and support ticketing systems.