Configure Max Email Size Limit in Office 365

Sending large files or attachments can pose a challenge, given that Microsoft 365/Office 365 has default limits on the size of emails that can be sent and received. In this blog post, we will delve into the process of configuring the maximum email size limit in Microsoft 365. This will provide you with greater flexibility and control over your email communications.

If you find yourself needing to send large reports, presentations, or media files, this guide will assist you in configuring the maximum email size restriction settings. You can set the maximum email size for sending and receiving using the Exchange admin center or PowerShell.

Before proceeding with the steps, it’s essential to understand the default configurations in Microsoft 365/Office 365 for all users. The default maximum size for sent messages is 35 MB (35840 KB), and for received messages, it is 36 MB (36864 KB).

For most organizations and users, default email size restrictions work well, and there’s usually no need to modify these values. However, in certain cases, such as when dealing with large reports from clients or automated scripts, you might consider adjusting these values to meet specific requirements.

The maximum size for sent and received messages can be set to 150 MB (153600 KB). Setting it beyond this value will result in a Non-Delivery Report (NDR). It’s important to note that setting a higher value for sent and received emails, does not guarantee email delivery. The successful transmission also depends on the destination server’s restrictions for sent and received email message sizes.

For example, if you have increased the value of the maximum size for sent email messages to 150 MB and send an email to an external email address with a size of, let’s say, 50 MB, the email may leave your tenant. However, if the destination server either does not accept large emails or has email message size restrictions in place, your email is likely to be rejected.

While increasing the maximum email size limit in Office 365 can offer greater flexibility in sending and receiving larger files, it’s important to be aware of some potential drawbacks before making this change:

  1. Storage limitations: Enabling larger email attachments may result in increased utilization of storage space on your email server, potentially leading to higher storage costs. The default Exchange Online mailbox size is 100 GB.
  2. Network congestion: In addition, sending large email attachments can contribute to network congestion and slow down your email system, impacting overall productivity.
  3. Compatibility issues: Some email systems may face challenges in handling larger attachments, potentially causing compatibility issues when sending or receiving emails with those systems.
  4. Security risks: Moreover, larger email attachments can pose a security risk if they contain sensitive or confidential information. Raising the max email size limit may increase the potential for hackers to infiltrate your system or for employees to inadvertently send confidential information outside of your organization.

Method 1 – Configure Sent and Received Emails Max Size Limit

You can utilize the Exchange admin center to set the maximum sent and received email size limit. This change can be applied either per mailbox or for all users at once. Let’s explore both methods.

1. Update Sent and Received Emails Max Size limit Per Mailbox

  • Log in to the Microsoft Exchange admin center as a Global administrator or Exchange Administrator.
  • Navigate to Recipients > Mailboxes and select any User Mailbox.
  • Click on Mailflow settings > Message size restrictions.
  • Alternatively, you can also click on the Mailbox to open the User Mailbox properties pane, go to the Mailbox tab, and then click on Manage message size restriction.
Update Sent and Received Emails Max Size limit per mailbox
Update Sent and Received Emails Max Size limit per mailbox
  • Modify the values for Sent messages maximum size (KB) and Received messages maximum size (KB), providing the new values in kilobytes (KB). For instance, to increase the sent and received email size to 50 MB, set it to 51200 KB.
Update Sent and Received Emails Max Size limit per mailbox
Update Sent and Received Emails Max Size limit per mailbox

2. Update Sent and Received Emails Max Size limit for All Mailboxes

  • To efficiently update the Sent messages maximum size (KB) and Received messages maximum size (KB) values for all users simultaneously, follow these steps:
    • Select all users by using the ‘Select All’ checkbox.
    • Update the message size restriction values as needed.
  • Log in to the Microsoft Exchange admin center as a Global administrator or Exchange Administrator.
  • Click on Recipients > Mailboxes and check the top checkbox next to ‘Display name‘ to select all mailboxes.
  • Click on Mailflow settings > Message Size restriction.
Update Sent and Received Emails Max Size limit for All Mailboxes
Update Sent and Received Emails Max Size limit for All Mailboxes
  • As evident from the Message Size Restriction settings pane, it indicates ‘Apply these changes to the 18 selected recipients‘ signifying that the Sent and Received message size you set will be applied to all 18 selected users simultaneously.
  • Configure the new value here. For example, to set the Sent and Received email max size to 50 MB for all users, set it to 51200, which is a value in KB.
Update Sent and Received Emails Max Size limit for All Mailboxes
Update Sent and Received Emails Max Size limit for All Mailboxes

3. Configure Default Sent and Received Emails Max Size Limit

Now that you know how to set the sent and received email max size limit for individual user mailboxes and all users at once, consider the scenario of new users joining the organization. Will they inherit the 50 MB limit or will the default 35 MB limit be applied?

The default limit of 35 MB will be applied, as new mailboxes inherit from the organization/tenant-level default max sent and received message limit restrictions. If you wish to set message size limit values for new users, you’ll need to update the default settings. Let’s explore how to perform this change:

  • Log in to the Microsoft Exchange admin center as a Global administrator or Exchange Administrator.
  • Click on Recipients > Mailboxes.
  • Click on Mailflow settings > Message size restriction.
Configure Default Sent and Received Emails Max Size Limit
Configure Default Sent and Received Emails Max Size Limit
  • On the ‘Default message size restriction‘ page, you can modify the values for ‘Sent messages maximum size (KB)‘ and ‘Received messages maximum size (KB)‘.
  • For Example, to establish a default sent and received message maximum size of 50 MB for any new user mailbox set the values to 51200 KB. Click ‘Save‘. Consequently, any new mailbox created will have the sent and receive message limit restrictions automatically set to 50 MB.
Configure Default Sent and Received Emails Max Size Limit
Configure Default Sent and Received Emails Max Size Limit

Method 2 – Configure Sent and Received Emails Max Size Limit using Powershell

If you prefer using the command line to update the sent and received email max size limit, you can also leverage PowerShell cmdlets. Initially, you would need to install the Exchange Online PowerShell module and then connect to Exchange Online with administrator rights.

Install Exchange Online Powershell Module

Install-module -Name ExchangeOnlineManagement

Connect to Exchange Online

Connect-ExchangeOnline

Example: Check Max Sent and Receive Email size Limit for [email protected]

Get-Mailbox -Identity [email protected] | ft MaxSendSize, MaxReceiveSize
Check Max Sent and Receive Email size Limit for AlexW@techpress.net
Check Max Sent and Receive Email size Limit for [email protected]

Example: Configure Max Sent and Receive Email Size Limit for [email protected] to 150MB

Set-Mailbox -Identity [email protected] -MaxSendSize 150MB -MaxReceiveSize 150MB
Configure Max Sent and Receive Email Size Limit for AlexW@techpress.net to 150MB
Configure Max Sent and Receive Email Size Limit for [email protected] to 150MB

Example: Set Max Sent and Receive Email Size Limit for All users to 150 MB

Get-Mailbox -Resultsize Unlimited | Set-Mailbox -MaxReceiveSize 150MB -MaxSendSize 150MB

Configure Default Max Sent and Receive Email Size Limit Using Powershell

Initially, we need to check the default mailbox plan, and then update the default mailbox plan properties for message size restrictions. Let’s explore how to perform this change:

Get-MailboxPlan

Get-MailboxPlan | ft name,isdefault
Get-Mailboxplan default
Get-MailboxPlan

Set-MailboxPlan

Set-MailboxPlan ExchangeOnlineEnterprise-3ebbec61-68ac-44d2-a506-d5577b7ec55a -MaxSendSize 150MB -MaxReceiveSize 150MB

Get-MailboxPlan ExchangeOnlineEnterprise-3ebbec61-68ac-44d2-a506-d5577b7ec55a | ft name, maxsendsize, maxreceivesize
Set-MailboxPlan to increase max send and receive email size
Set-MailboxPlan

Error When Exceeding Message Size Limit Restrictions

You may receive a Non-Delivery Report (NDR) email if you encounter issues sending or receiving large emails. The following email was generated by the system when someone attempted to send a 46MB email to me.

Your message wasn’t delivered to anyone because it’s too large.
The limit is 35 MB. Your message is 36 MB.

Jatin Makhija ([email protected])
Your message couldn’t be sent because it’s too large.

Diagnostic information for administrators:
Generating server: XXXX.GBRP123.PROD.OUTLOOK.COM
[email protected]
Remote server returned ‘550 5.2.11 RESOLVER.RST.SendSizeLimit.Sender; message size (35884 KB) too large for this sender with limit 35840 KB’
Original message headers:
<<message header information>>>

Conclusion

By following the steps outlined in this blog post, you can establish appropriate limits for email attachments within your organization, thus preventing unnecessary delays and rejections of emails.

If you are increasing the size limits and sending an email internally, it should generally be fine, resulting in fewer rejected emails. However, when sending large emails to another organization, please note that the reception may vary. The third-party email server may or may not accept the email, depending on their email message size restrictions, which they have set according to their requirements.

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