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Outlook 2016 - Tutorial for Beginners - 2017 How To Use Microsoft Outlook on Office 365 Windows 10 - Duration: 9:59. Professor Adam Morgan 211,478 views.

1. Font Size In Office 365

Microsoft has announced that Office 365 (Exchange Online) now supports up to 150MB email messages. This is quite a large increase from the previous limit of 25MB (actually 35MB, I'll explain why shortly) and no doubt will be a welcome change for many customers.

The previous limits were a deployment blocker for some customers that I've worked with who either had a higher limit for their general user population (often more like 50MB) or who had a few specific mailboxes that needed to receive very large emails (often a system-monitored mailbox). While I am generally of the opinion that email is a poor transport mechanism for large files I can understand how the modern era of fast networks, cheap storage capacity, and the convenience of email all come together to create the situation where large email attachments become a requirement.

Font Size In Office 365

Before we go any further let me point out that just because you can set a message size limit of 150MB, it doesn't mean you necessarily should. By all means increase the message size limit to suit your business, but don't just crank it right up to 150MB for the sake of it. Consider the impacts this will have on your network bandwidth, client performance, on-premises infrastructure (if you're running a Hybrid configuration), journalling, and the fact that you'll more often than not find that other companies you're emailing support a far smaller message size limit. All of this may actually lead to a poor experience for your users, and an increase in support requests for you.

I suspect the new 150MB limit is not due to Microsoft endorsing the use of email for sending big files. The more likely reason in my view is that it is large enough number to completely silence any customer complaints (and therefore remove the burden of those support calls) about the previous limits.

With that said, let's look at how you can configure the message size limit in Exchange Online.

Comparisons with On-Premises Exchange Server

As many of you already know there are multiple places that message size limits can be applied for an on-premises Exchange Server environment. These include:

• Organization-wide transport config
• Send/receive connectors
• AD site links
• Individual recipients

As a general rule organizations tend to apply a consistent limit across all of those settings, however the capability is certainly there to customize the configuration to suit nearly any scenario that arises (for example, preventing large email messages from being sent to very large distribution groups).

With Exchange Online we get far less administrative control as the customer than we do for on-premises Exchange. There's no access to send/receive connectors or AD site links. And although we can see the transport configuration (which has unlimited max send/receive limits) we can't make any changes to those settings.

Interestingly I seem to have one mailbox there with no mailbox plan. As it turns out that is the discovery search mailbox, so we don't need to worry about that one.

Remember, you'll need to determine the exact name of your mailbox plan when you run that command.

Managing Message Size Limits for Existing Mailboxes

Although I've updated my mailbox plan above, existing mailboxes still have the previous settings applied. A change to the mailbox plan has no impact on existing mailboxes.

Naturally that means you can update any subset of your users by filtering the output of Get-Mailbox first. If you're not sure, just run your Get-Mailbox command first and make sure it is only returning the mailboxes you want to modify before you start piping it into Set-Mailbox.

Message Size Limits != Attachment Size Limits

As always you need to be aware that this setting controls the maximum message size, not the maximum attachment size. An email message is bigger than just the files that are attached to it, thanks to the message content itself as well as other data that is piled on. Or as Microsoft describes it, “overhead needed for encoding, encapsulation, compression and decompression of larger messages.”

This is why the previous Exchange Online message size limit of 25MB was actually implemented as a 35MB limit. 25MB was advertised on the Exchange Online service description, but the extra 10MB of growth allowance was added for growth allowance.

In your career as an email administrator you'll have many conversations with an end users about this. Just remember to include that growth allowance when configuring the maximum message size, because whatever you tell your users will inevitably be interpreted by them as the maximum attachment size.

Additional Notes

Microsoft limits our administrative control in Exchange Online in many interesting ways. For example, we can use Set-MailboxPlan to modify the max send/receive message sizes, but many of the other mailbox plan settings can't be modified.

Also, Microsoft limits the values that we can set for max send/receive message size. For example, if I try to set the limit to 200MB I get this error.