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Microsoft Expands Office 365 Message Size Limit to 150MB

Microsoft has increased the maximum size of an e-mail message that can be sent by an organization using its cloud-based Office 365 services to 150MB.

Previously, a single Office 365 e-mail message could be 25MB max. Microsoft now permits IT pros to specify the permitted size of a message, which can range between 1MB to 150MB.

IT pros can change these settings for individual users via Office 365's Exchange Admin Center. However, if many users are involved, Microsoft recommends using PowerShell commands to get the job done, particularly if an organization supports more than 1,000 users.

Microsoft listed the PowerShell commands to get that done in its announcement this week. The expanded e-mail size capability already has been rolled out. It's currently available for Office 365 subscribers, according to a Microsoft spokesperson. Microsoft's e-mail service in Office 365 runs off its Exchange Online service, which is included in some plans for businesses, including "Business Premium," "E1" and "E3" plans.

Expanding the e-mail size limit involves updating a bunch of mailboxes, which can take about five minutes to 10 minutes for each 1,000 users. Next, there's a 15-minute period in which the updates get replicated across the service. Lastly, Microsoft recommends waiting "up to 30 minutes" after the update process completes before testing the changes.

Microsoft cautioned IT pros that message sizes can grow 33 percent larger if they pass between premises-based Exchange environments and cloud services because of a "transcoding" process that bulks up the message. In such cases, the max message size should be limited to around 112MB max. Messages sent within the Office 365 service, though, don't undergo this transcoding process, and can be set at the 150MB max limit.

Organizations using Microsoft's Outlook Web App client application to send e-mails have some further considerations. The Outlook Web App assumes a transcoding hit of 25 percent. Microsoft's example is that if the Office 365 e-mail size limit has been set to 100MB, the Outlook Web App only will be able to send a message that's 75MB in size max.

In addition, the Outlook Web App has an attachment size limitation. Each attached file can't exceed 25MB. Microsoft's announcement noted, though, that "these conditions may change in the future."

The maximum file size for organizations using premises-based Exchange Server hasn't changed with Microsoft's Office 365 announcement this week. It's still limited to 10MB max per e-mail, as Microsoft outlines in this TechNet article. Hybrid Exchange users (those organizations using Exchange Server and Exchange Online in combination) typically leave the max size at 10MB to have a consistent size across both environments, according to the Microsoft spokesperson.

About the Author

Kurt Mackie is senior news producer for the 1105 Enterprise Computing Group.

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