The following limits currently exist for Exchange Online Protection. These limits aren’t configurable unless specified otherwise.
Tip
For more information about limits in Exchange Online, see Exchange Online limits. The transport rule limits also apply to EOP standalone customers. The recipient rate and message rate limits for Exchange Online aren’t applicable for EOP standalone customers.
Accepted domain limit - You can add up to 5000 accepted domains per tenant. Subdomains can be included in this 5000-limit, or if necessary, as part of a catch-all option, match subdomains. For more information, see Manage Accepted Domains in EOP.
Remote domain limit - You can add up to 200 remote domains per tenant.
Message size limit - The maximum message size for EOP standalone customers, including attachments, is 150 MB.
Number of outbound messages sent - The limit for the number of outbound messages sent through EOP is high enough to ensure that normal email communication isn’t treated as spam. If you want to send commercial bulk email messages, rather than sending outbound messages through EOP, we recommend that you either use a third-party email service provider (ESP) or send them through your on-premises email servers.
Recipient limit - As long as the sending host can split the message into "chunks" of fewer than 500 recipients, no explicit limit is defined. However, each "chunk" is effectively treated as a new message. Too many messages in a short period, messages from a host with a poor reputation, or messages with questionable content could be throttled or blocked.
IP Allow or IP Block list limit - When configuring an IP allowlist or an IP blocklist in the connection filter, you can specify a maximum of 1273 entries, where an entry is either a single IP address or a CIDR range of IP addresses from /24 to /32.
Message deferral limit - Messages in deferral will remain in our queues for 24 hours. Message retry attempts are based on the error type received from the recipient's mail system. Messages are retried every 15 minutes.
Spam quarantine retention period - By default, spam messages sent to the quarantine are retained for 30 days. Administrators can lower this value via content filter policies.
End-user spam quarantine notifications - By default, if enabled, end-user spam quarantine notifications are sent every 3 days. They can be configured to be sent every 1 to 15 days.
Find the Exchange Online limits for various service areas, including address book limits, mailbox storage limits, and reporting and message trace limits, to name just a few.
Learn about the exchange online protection feature details like recipient, domain, and company management, Messaging policy and compliance, Mail flow and Anti-spam and anti-malware protection.
Fixes an issue in which you receive a The rule can't be created because it is too large error message when you try to create or change a transport rule in Exchange Online or in Exchange Online Protection.
Obtain information about features and requirements for Exchange Online Protection. Included is a list of plans that provide Exchange Online Protection, as well as a comparison of features across those plans.
This module examines how Exchange Online Protection (EOP) protects organizations from phishing and spoofing. It also explores how EOP blocks spam, bulk email, and malware before they arrive in users’ mailboxes.