By default, with a Microsoft email account, you’re allowed to send or receive emails not larger than 25 MB. While there are good reasons for such a small attachment limit, many users wish want to change this default setting. In the following tutorial, we’ll quickly explain how you can easily change the Office 365 attachment size and set the message size limit for one or all users.
Summary:
The Office 365 maximum message size setting determines the maximum size of an email that can be sent or received, including attachments. The default setting is 25 MB and can be changed in the Exchange admin center or via PowerShell to up to 150 MB. You may want to change the default value to prevent common errors when sending / receiving large files or when performing an email migration to Microsoft 365.
➡️ A step-by-step tutorial on how to change the Office 365 max file size for one or multiple users can be found here.
Easily Explained:
What’s the Office 365 Max Message Size Limit?
✅ The Office 365 max message size limits determines the maximum allowed size of an email, including attachments.
How does the MS 365 Message Size Limit Work?
The max message size limit prevents you from receiving or sending emails with attachments that are larger than the select maximum value. This means, if your mailbox is configured with the default value of 25 MB, you can send or receive an email that contains a 24 MB attachment. However, what you cannot do, is send or receive an email with an attachment that is larger than 25 MB.
❓ But is 25 MB a reasonable limit or should you change the maximum message size?
Reasons to Increase the Maximum Message Size:
It’s a good idea to increase the maximum message size for your MS 365 mailbox if one of the following scenarios applies:
- you’re regularly receiving emails with large attachments
- you often need to send emails with large attachments and are sure that the recipients are also able to receive large messages
- you’re migrating your emails to MS 365 and your old account contains emails that are larger than Microsoft’s default value
Reasons to Decrease the Maximum Message Size:
On the other hand, there are also good reasons to decrease the maximum message size:
- you’re managing an MS 365 account for your company / institution and do not want every user to be able to send large files (Think: schools that want to prevent their students from sending large attachments)
- you do not want to restrict the overall mailbox size, but wish to prevent your users from using their email accounts as storage space for large files
- you’re regularly sending emails to recipients that cannot receive large attachments
❓ So what happen’s when you send or receive an email that is larger than the default value?
Common Error Messages when Exceeding the Message Size Limit:
If you receive or sent an email that is larger than the message size limit, the email is rejected and you’ll receive one of the following error messages:
⛔️ Maximum size of appendable message has been exceeded
⛔️ Attachment size exceeds the allowable limit
⛔️ 552: Message size exceeds the maximum permitted
⛔️ System Undeliverable, message size exceeds outgoing message size limit
⛔️ The message was not sent; reduce the message size and try again
⛔️ 552 5.3.4 Message size exceeds the fixed maximum message size
⛔️ Error 0x80040610: The message being sent exceeds the message size established for this user
Office 365 Maximum Message Size andEmail Migration
Receiving a “maximum message size exceeded error” is a common scenario when performing an email migration to Microsoft 365.
Many mail servers allow a much larger maximum message size limit than Microsoft’s default value. Therefore, after performing your mail migration to MS 365, it’s possible that some large emails could not be migrated to your Office 365 mailbox.
When performing an email migration to Office 365 with MailJerry and your old mailbox contains large emails, you’ll find one or more error message similar to this one in your migration summary:
INBOX/841 {42026170} could not append ( Subject:[=?GBK?B?yczStbrP1/c=?=], Date:["14-Mar-2023 07:16:39 +0000"], Size:[42026170], Flags:[\Seen] ) to folder INBOX: Error sending 'APPEND INBOX (\Seen) "14-Mar-2023 07:16:39 +0000" {42026170}': 40 NO Maximum size of appendable message has been exceeded
How to Migrate Emails to Office 365 that Exceed the Max Message Size Limit:
If you wish to migrate emails that are larger than the current Office 365 maximum value, simply perform these three steps:
1. Increase the max message size limit following the steps explained below.
2. Wait for about 30 minutes so that Microsoft’s system has enough time to deploy the new settings.
3. Open your migration in MailJerry, scroll down to Options and click on Sync Now.
✅ The software will now migrate the missing emails to Office 365.
How to
Change the Office 365 Max Message Size Limit
The preferable way to change the maximum attachment / message size limit for one or multiple accounts is by using the Exchange admin center. Here’s how it works:
Change the Max Message Size Limit for one User:
1. Log in to the Exchange admin center at https://admin.exchange.microsoft.com/
2. Go to Recipients > Mailboxes.
3. Click on the user name of the mailbox you wish to change.
4. In the overlay that opens, open the tab Mailbox. Here, click on Manage message size restriction.
5. In the fields Sent messages maximum size and Received messages maximum size, enter the desired maximum size in KB. The maximum possible value is 153600.
If you’re unsure which value to enter to set the desired maximum in MB, you can refer to this KB to MB Converter.
6. Confirm your changes by clicking on Save and you’re done!
How to Set the Office 365 Message Size Limit for all Users:
To change the max message size limit for multiple or all users, follow these steps:
1. Log in to the Exchange admin center at https://admin.exchange.microsoft.com/
2. Go to Recipients > Mailboxes.
3. Select all mailboxes you wish to edit.
4. In the tob bar, klick on Mailflow settings and select Message size restriction.
5. An overlay opens. Here, enter the new limit in KB in the fields Sent messages maximum size and Received messages maximum size.
6. Klick on Save to save your changes.
Alternative Method:
How to Change the Office 365 Max Message Size via PowerShell
While the Exchange Admin Center offers a great way to change the maximum message size for one or multiple users, managing the allowed attachment size for 100 or more accounts at once is easier achieved by using the Microsoft PowerShell.
Here’s how it works:
1. Log in to your Office 365 account using this PowerShell command:
$Cred = Get-Credential
Press Enter and enter your username and password.
2. Now enter the following two commands to start a new session:
$Session=New-PSSession –ConfigurationName Microsoft.Exchange –ConnectionUri https://ps.outlook.com/powershell/ -Credential $Cred –Authentication Basic –AllowRedirection
Import-PSSession $Session
3. Update one or multiple mailboxes using one of the following commands:
Update the max message size for one mailbox:
Set-Mailbox –Identity your@email.com –MaxSendSize 150MB – MaxReceiveSize 150MB
Update multiple mailboxes:
("username01", "username02", "username03") | % {Set-Mailbox –Identity $_ -MaxSendSize 150MB -MaxReceiveSize 150MB}
Update all mailboxes:
Get-Mailbox | Set-Mailbox -MaxSendSize 75MB -MaxReceiveSize 75MB
Update the default settings:
This setting applies for all mailboxes that you’re going to create in the future.
Get-MailboxPlan | Set-MailboxPlan -MaxSendSize 150MB -MaxReceiveSize 150MB
➡️ Usually, it takes 15 minutes until the new Office 365 max message size limit is applied across all services, however, Microsoft recommends to allow up to 30 minutes before testing the new settings.
Frequent Questions:
Office 365 Max Message Size
I’ve set the Office 365 message size to 150 MB, still, I cannot send / receive emails larger than 112 MB. What’s wrong?
Changing the max message size limit to 150 MB does not necessarily man that you’re allowed to send / receive emails of this size. When emails are sent from one mail server to another, they’re transcoded based on the settings of the involved mail systems. This may result in a message being 33% larger than the original email size. Therefore, if an email server is involved in your email communication that uses BASE64/MIME conversion, your actual maximum message size is limited to 112 MB.
Is the maximum message size limit of 150MB supported by all email clients?
When working with Outlook, Apple Mail or Thunderbird, you can send / receive emails up to 150 MB. This is also true when performing an email migration.
The limit for the Outlook Web Application is 112 MB, even if you’ve set your maximum message size limit to 150 MB.
When working with Outlook for iOS and Android, the limit is even set to a smaller maximum of 33 MB.
Is it always a good idea to use the maximum message size limit of 150 MB for my account?
No. Actually, setting the limit to the allowed maximum value is only a good idea if you:
- need to migrate large emails to your Office account
- regularly send / receive emails with large attachments (think of architects or designers)
- are sure that your recipients email systems are able to receive emails with large attachments
- are only working with email clients that support large message sizes (e.g. Outlook, Thunderbid, Apple Mail…)
➡️ In all other use cases, it’s better to stick with a smaller limit.
What’s the ideal maximum message size limit?
The ideal maximum message size limit for your Microsoft 365 account depends on your personal preferences and email communication habits. For convenient email communication and a high rate of email deliverability a limit between 30 and 50 MB is suitable. This allows you to send one or two large files, but prevents you from sending huge files accidently.
➡️ In general, when exchanging large files, it’s always a good idea to use third party services like OneDrive, Google Drive or DropBox.
What’s the maximum number of attachments in MS 365?
When sending an email with your Office 365 email account, you can add up to 250 files as attachments. However, the total email size (= size of your message plus all attachments) may not exceed the maximum message size limit that is set for your account.
Does changing the max message size affect email delivery?
When sending or receiving an email with one or more large attachment, it takes longer until the message is transferred successfully. Furthermore, if you send a large email to a recipient with a smaller max message size limit, the email will be rejected and you’ll receive an error message.
Therefore, changing the maximum message size itself does not affect email delivery or email delivery time, but what you do with the enhanced possibilities of being able to work with larger attachments actually may.
