Treat the new Office 365 150 MB maximum message size with caution

I hope that the excitement that I heard voiced by many when Microsoft announced that Office 365 now allows the transmission of messages of up to 150 MB has quietened down. Sure, it’s nice to be able to send the manuscript of an entire book via email (something I did the other day with some glee), but some intractable problems exist that must be overcome before the new limit is really practicable.

The first issue is connectors. Office 365 is a big beast that supports upwards of a million tenants at this point, all of whom can merrily send ginormous messages to each other. However, once email seeks to escape from the walled garden of the service, it has to travel across connectors to other systems like Gmail, Yahoo! Mail, or on-premises email. Although I am sure the administrators of email systems outside Office 365 applaud the new maximum, they might decide that such large messages are not well suited for their systems and restrict messages to what might be deemed a more reasonable limit, like the old 25 MB limit used by Office 365. Thus, any message sent outside Office 365 that surpasses the 25 MB threshold will be promptly rejected by its destination. This, in turn, will lead to user unhappiness because their mail won’t get through.

The next question is whether we want users to send each other gigantic tomes. It seems to me that Microsoft takes a dual-headed approach here, possibly to facilitate the particular email habits of all. On the one hand, they up the maximum message size. On the other, they preach the wisdom of "modern" attachments, meaning that you shouldn’t really send such large attachments at all. The adherents of modern messaging include links to documents stored in OneDrive instead and solve the horrible problem of attachment anarchy, meaning that those involved in co-editing a document might have to cope with different versions of the document circulating as attachments. A plethora of methods to share attachments are available today without cluttering mailboxes with massive files.

Another point of interest is the impact on infrastructure. Inside Office 365, Microsoft has scads of fiber networks to transport massive messages between its datacenters and even more disks to store the files. After all, 150 MB messages are a good way of filling those 50 GB mailbox quotas, not to mention the other 50 GB available in the archive mailbox. But let’s think of what happens when some poor user has the misfortune to attach half a CD’s worth of information to a message that is then sent as a reply all to a large distribution list. Even Office 365 users might be perturbed by the need to download this kind of correspondence as Outlook synchronizes the Inbox across a flaky WiFi connection.

Even Microsoft’s infrastructure might not escape the effect of such poor use of email. After all, the recently announced Advanced Threat Protection (ATP) add-on for Exchange Online Protection might be called upon to examine 150 MB attachments to determine whether they contain a day zero virus. According to some who have been testing ATP (still only available in preview in the U.S.), the passage of a suspicious message through examination can delay its delivery by 30 minutes or more. Processing speed is likely to improve as Microsoft spins up ATP for worldwide availability, but the resources that might be required to process huge chunks of suspicious content could be significant if delivery times are to be kept to a reasonable limit.

Finally, there are user bad habits to consider. Of course, users with bad habits are few and far between, but they do exist. A long time, when digital photography was in its infancy, I had a problem with a senior executive who insisted in inserting a photo of his new baby in his autosignature, thus incurring a penalty of several hundred kilobytes of baby per message. That problem was solved when the executive quickly exhausted his mailbox quota. Given the multi-megabyte photos generated today, you can see how a similar error in judgment could lead to a huge amount of duplicated information circulating in email. After all, if you’ve seen one baby photo, haven’t you seen them all? Actually, the same point is true for the corporate logos that many insist should be inserted into their autosignatures...

Before we all rush to increase message size limits for tenants, perhaps some reflection is necessary to figure out whether this is in fact a good idea. It might be for users who have a business need to circulate large files such as architectural designs, but I hazard a guess that the older 25 MB limit is just fine for the majority. Indeed, as I found out when I sent the Word and PDF files for the "Office 365 for Exchange Professionals" eBook to Microsoft, that 60 MB message was rejected by their dedicated Office 365 tenant, so even Microsoft doesn't quite go the whole hog with this feature.

Although Outlook is happy to send large attachments, it's true that some clients might not be able to process massive attachments, so testing is required before you unleash a larger limit on users.

Overall, while some companies will be very interested in massive attachments, the bottom line is that unless you can clearly describe an obvious business need, it just doesn’t seem to make much sense to rush a six-fold increase in the maximum size of a message.

Follow Tony @12Knocksinna

PS. In other news, the ex-Acompli team reached a notable milestone yesterday when Outlook for Android came out of preview status and is now regarded as a fully-fledged member of the Outlook family. This is easily the best client for Exchange that's available on Android, even if all of the issues identified earlier this year have not yet been addressed.