Exchange Online (Office 365) Limits : What to Know

Read time: 8 minutes

Every Office 365 mailbox, sender, recipient, and attachment has specific limits, which must be respected. Limits on the number of recipients per message, message size, and attachment size also have a direct impact on your business, migrations, and day-to-day operations.

The Exchange Online limits may cause message delivery failures, email delays, or account lockouts. In this blog, we will discuss various Exchange Online email limits and provide updated values. Read on to optimize your Office 365 email configuration.

Why Do Exchange Online Limits Exist?

Exchange Online email limits are not there to restrict you, but to keep the service secure, fast, and fair for everyone. Here are the top reasons why Microsoft enforces these limits:

Prevent spam, abuse, and malicious bulk sending
Make sure fair resource use for all tenants
Protect servers from overload and unexpected outages
Maintain consistent email delivery performance and reliability
Control storage costs and optimize server capacity
Enforce security policies and reduce phishing risks

Mailbox Storage Limits

The mailbox storage limits are different for each mailbox type, like a primary mailbox, archive mailbox, shared mailbox, group mailbox, etc. And it depends on the subscription plan too. Here is the table-

Plan\mailbox	User Mailbox	Archive mailbox	Shared mailbox	Resource mailbox	Public folder mailbox	Group mailbox
Office 365 Business Basic and Standard	100 GB	50 GB	50 GB	50 GB	100 GB	50 GB
Office 365 Business Premium	100 GB	1.5TB	50 GB	50 GB	100 GB	50 GB
Office 365 Enterprise E1	50 GB	50 GB	50 GB	50 GB	100 GB	50 GB
Microsoft 365 Enterprise E3/E5	100 GB	1.5TB	50/100 GB	50 GB	100 GB	50 GB
Office 365 Enterprise E3/E5	100 GB	1.5TB	50/100 GB	50 GB	100 GB	50 GB
Office 365 Enterprise F3	2 GB	NA	50 GB	50 GB	100 GB	50 GB

But keep in mind that Office 365 administrators can reduce these limits as per the organization’s requirements.

Message Limits

The message limits apply to each message for various parameters like message size limit, subject length limit, file attachment limit, attachment size limit, multipart message limit, and embedded message depth limit.

The values below are the maximum limits. By default, mailboxes can send messages up to 35 MB and receive messages up to 36 MB. Office 365 administrators can change (increase or reduce) these limits per their needs, within the allowed range of 1 MB to 150 MB for message size.

Mailbox/Plan	Office 365 Business Basic and Standard	Office 365 Business Premium	Microsoft 365 Enterprise E3/E5	Office 365 Enterprise E1	Office 365 Enterprise E3/E5	Office 365 Enterprise F3
Message size limit-Outlook	150 MB	150 MB	150 MB	150 MB	150 MB	150 MB
Message size limit-OWA	112 MB	112 MB	112 MB	112 MB	112 MB	112 MB
Message size limit-Outlook for Mac	150 MB	150 MB	150 MB	150 MB	150 MB	150 MB
Message size limit-migration	150 MB	150 MB	150 MB	150 MB	150 MB	150 MB
Message size limit-Outlook for iOS and Android	33 MB	33 MB	33 MB	33 MB	33 MB	33 MB
Subject length limit	255 Characters	255 Characters	255 Characters	255 Characters	255 Characters	255 Characters
File attachment limit	250 attachments	250 attachments	250 attachments	250 attachments	250 attachments	250 attachments
File attachment size limit- Outlook	150 MB	150 MB	150 MB	150 MB	150 MB	150 MB
File attachment size limit- OWA	112 MB	112 MB	112 MB	112 MB	112 MB	112 MB
File attachment size limit- Outlook for Mac	150 MB	150 MB	150 MB	150 MB	150 MB	150 MB
File attachment size limit-New Outlook for Mac	150 MB	150 MB	150 MB	150 MB	150 MB	150 MB
File attachment size limit- Outlook for iOS and Android	150 MB	150 MB	150 MB	150 MB	150 MB	150 MB
Multipart message limit	250 parts	250 parts	250 parts	250 parts	250 parts	250 parts
Embedded message depth limit	30 embedded messages	30 embedded messages	30 embedded messages	30 embedded messages	30 embedded messages	30 embedded messages

When the message size exceeds this limit, it is not delivered to the recipient. However, the sender will receive a non-delivery report. The advantage of setting an upper limit for the message size is that time is not wasted on the delivery of unusually large emails. Consequently, it helps in improving the delivery of normal messages and enhancing the overall performance.

Receiving and sending limits

These limits are intended to block spam and phishing messages in the Exchange environment.

Receiving limits

It is the number of messages that can be received per hour by a user, public folder, or group. After exceeding this limit, the mailboxes will not receive emails for an hour.

Plan\mailbox	Receiving limits	Messages received from single sender
Office 365 Business Essentials	3,600 messages/hour	33% of receiving limit
Office 365 Business Premium	3,600 messages/hour	33% of receiving limit
Office 365 Enterprise E1	3,600 messages/hour	33% of receiving limit
Office 365 Enterprise E3	3,600 messages/hour	33% of receiving limit
Office 365 Enterprise E5	3,600 messages/hour	33% of receiving limit
Office 365 Enterprise F1	3,600 messages/hour	33% of receiving limit

Sending limit

These limits apply to an Exchange Online account while sending messages:

Plan\mailbox	Recipient rate limit	Recipient limit	Recipient proxy address limit	Message rate limit	Recipient limit for encrypted messages
Office 365 Business Basic and Standard	10K per day	Customizable up to 1000 recipients	300	30 messages per minute	About 200 recipients
Office 365 Business Premium	10K per day	Customizable up to 1000 recipients	300	30 messages per minute	About 200 recipients
Office 365 Enterprise E1	10K per day	Customizable up to 1000 recipients	300	30 messages per minute	About 200 recipients
Microsoft 365 Enterprise E3/E5	10K per day	Customizable up to 1000 recipients	300	30 messages per minute	About 200 recipients
Office 365 Enterprise E3/E5	10K per day	Customizable up to 1000 recipients	300	30 messages per minute	About 200 recipients
Office 365 Enterprise F3	10K per day	Customizable up to 1000 recipients	300	30 messages per minute	About 200 recipients

Address Book limits

The Address Book limits apply not to an individual mailbox but to the Exchange organization. It defines the maximum number of address lists, offline address books, address book policies, and global address lists that can be created in an organization.

Plan\mailbox	Address List Limit	Offline Address Book Limit	Address Book Policies Limit	Global Address Lists Limit
Office 365 Business Basic and Standard Essentials	1K	250	250	250
Office 365 Business Premium	1K	250	250	250
Office 365 Enterprise E1	1K	250	250	250
Office Microsoft 365 Enterprise E3/E5	1K	250	250	250
Office 365 Enterprise E3/E5	1K	250	250	250
Office 365 Enterprise F31	1K	250	250	250

Capacity Alerts

Exchange Online provides three kinds of notifications when a user’s mailbox is nearing or at capacity, which are ‘Warning’, ‘Prohibit send’, and ‘Prohibit send/receive’.

Plan/Features	Warning	Prohibit send	Prohibit send/receive
Office 365 Business Basic and Standard	98 GB	99 GB	100 GB
Office 365 Business Premium	98 GB	99 GB	100 GB
Microsoft 365 Enterprise E3/E5	98 GB	99 GB	100 GB
Office 365 Enterprise E1	49 GB	49.5 GB	50 GB
Office 365 Enterprise E3/E5	98 GB	99 GB	100 GB
Office 365 Enterprise F3	1.96 GB	1.98 GB	2 GB

Distribution Group Limits

The following limits apply to distribution groups in your organization’s shared address book:

Plan/Features	Maximum number of distribution group members	Limit sending messages to large distribution groups	Maximum message size for distribution groups with 5,000 to 99,999 members	Maximum message size for distribution groups with 100,000 members	Maximum number of distribution group owners	Maximum number of groups a user can create
Office 365 Business Basic and Standard	100,000 members	5,000 or more members	25 MB	5 MB	100	300,000
Office 365 Business Premium	100,000 members	5,000 or more members	25 MB	5 MB	100	300,000
Microsoft 365 Enterprise E3/E5	100,000 members	5,000 or more members	25 MB	5 MB	100	300,000
Office 365 Enterprise E1	100,000 members	5,000 or more members	25 MB	5 MB	100	300,000
Office 365 Enterprise E3/E5	100,000 members	5,000 or more members	25 MB	5 MB	100	300,000
Office 365 Enterprise F3	100,000 members	5,000 or more members	25 MB	5 MB	100	300,000

So, these are some essential limits Office 365 administrators need to be aware of. These limits are quite high, and administrators do not need to pay any attention to them, as efficient communication can be achieved within the available limits. However, it is a good practice to keep a watchful eye on how Exchange resources are being used in the organization.

When Part of Your Mail Still Runs on Exchange Server

The limitations of Exchange Online apply to mailboxes in Microsoft 365. For organizations that use on-premises

Exchange Server, limits are defined by the administrator; mailbox size and growth, email traffic, and OWA usage should be monitored by analyzing the server’s logs and information stores. Kernel Exchange Reporter generates 80+ detailed reports on email flow, OWA access, and mailbox activities. You can schedule scans to run daily, weekly, or monthly, and save the results as Word, PDF, CSV, and HTML. It creates different graphs and reports that enable you to optimize the available resources and enhance performance.

Free Download 100% Secure

Final Words

Office 365 email limits are crucial for your day-to-day communication. Mailbox size limits, message size limits, and throttling policies are there to make sure of proper Exchange Online usage and protection of your data. Knowledge of Exchange Online limits and their regular checking are obligatory for every Exchange Online administrator.

Frequently Asked Questions

Q. What are Exchange Online limits?

Ans. Exchange Online email limits control mailbox storage, message size, sending/receiving volumes, and directory structure across Microsoft 365 plans.

Q. What happens when you hit Exchange Online limits?

Ans. Hitting Exchange Online limits triggers specific automatic actions depending on whether you exceed storage, sending, or receiving thresholds.