Various email limits in Exchange Online (Office 365)

Aftab Alam    Aftab Alam     Published On - 14 May 2019

Office 365 is the dominant cloud service platform and is provided by Microsoft, which has given it a leverage over its counterparts. There are more than 150 million active users for Office 365, and still is increasing at a rapid speed. It provides us the impression that it can handle a vast number of emails than a regular email server and yes, it is true. However, Office 365 has different storage limits and different email/contacts limits for different plans. And these limits vary based on the subscription plans.

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 Site mailbox Public folder mailbox Group mailbox
Office 365 Business Essentials 50 GB 50 GB 50 GB 50 GB 50 GB 50 GB 50 GB
Office 365 Business Premium 50 GB 50 GB 50 GB 50 GB 50 GB 50 GB 50 GB
Office 365 Enterprise E1 50 GB 50 GB 50 GB 50 GB 50 GB 50 GB 50 GB
Office 365 Enterprise E3 100 GB Unlimited 50 GB 50 GB 50 GB 100 GB 50 GB
Office 365 Enterprise E5 100 GB Unlimited 50 GB 50 GB 50 GB 100 GB 50 GB
Office 365 Enterprise F1 2 GB NA 50 GB 50 GB NA NA 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, header size limit, subject length limit, file attachment limit, attachment size limit, multipart message limit, and embedded message depth limit.

Office 365 administrators can change (increase or reduce) these limits are per their needs.

Plan\mailbox Message size limit – Outlook Message Size Limit – OWA Message Size Limit – Outlook for Mac Message Size Limit – Migration Subject length Limit
Office 365 Business Essentials 150 MB 112 MB 150 MB 150 MB 255 char
Office 365 Business Premium 150 MB 112 MB 150 MB 150 MB 255 char
Office 365 Enterprise E1 150 MB 112 MB 150 MB 150 MB 255 char
Office 365 Enterprise E3 150 MB 112 MB 150 MB 150 MB 255 char
Office 365 Enterprise E5 150 MB 112 MB 150 MB 150 MB 255 char
Office 365 Enterprise F1 150 MB 112 MB 150 MB 150 MB 255 char

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 message 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 Message Received
Office 365 Business Essentials 3,600 messages/hour
Office 365 Business Premium 3,600 messages/hour
Office 365 Enterprise E1 3,600 messages/hour
Office 365 Enterprise E3 3,600 messages/hour
Office 365 Enterprise E5 3,600 messages/hour
Office 365 Enterprise F1 3,600 messages/hour

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
Office 365 Business Essentials 10K per day 500 recipients 400 30 messages per minute
Office 365 Business Premium 10K per day 500 recipients 400 30 messages per minute
Office 365 Enterprise E1 10K per day 500 recipients 400 30 messages per minute
Office 365 Enterprise E3 10K per day 500 recipients 400 30 messages per minute
Office 365 Enterprise E5 10K per day 500 recipients 400 30 messages per minute
Office 365 Enterprise F1 10K per day 500 recipients 400 30 messages per minute

Address Book limits

The Address Book limits apply not to an individual mailbox but the Exchange organization. It defines the maximum number of address lists/offline address books/address book policies/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 Essentials 1K 250 250 250
Office 365 Business Premium 1K 250 250 250
Office 365 Enterprise E1 1K 250 250 250
Office 365 Enterprise E3 1K 250 250 250
Office 365 Enterprise E5 1K 250 250 250
Office 365 Enterprise F1 1K 250 250 250

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 give any attention to it 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. But, effective Exchange features are not available to monitor the usage of Exchange resources. So, one has to rely on professional tools like Kernel Exchange Reporter for the same.

Final words

If you want to get granular information on the resource consumption in your Exchange Server environment, then you should use the Kernel Exchange Reporter tool which brings detailed information. It creates different graphs and reports which enable you to optimize the available resources and enhance performance.

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