Skype for Business on Mac finally got file transfer capability in April. Then, just last week, a co-worker asked me about a thorny issue they’ve had with file transfers intermittently failing. (I’ll cover this in its own post once we’ve fully diagnosed and fixed the problem.)

Both these items led me on a stroll through the technology behind file transfer in Skype for Business. I consider the ability to send/receive files a fundamental function…and I’m certainly not the only one. Comments on SkypeFeedback.com and Office 365′ Feedback Forums echo its importance among my fellow Skype4B users.

Let’s take a dive into what goes into file transfer, shall we? It doesn’t need much configuration…but like air, you notice when it’s not there!

Where Can You Transfer Files in Skype for Business?

File Transfer is a basic part of Skype for Business, both Server and Online. As the Skype admin, you control whether users can or cannot send files to one another, and through which tools.

The most common file transfer method is through Instant Messaging (or “P2P File Transfer”). However, you can also share files in a Skype Meeting.

File Transfer is enabled by default. But in case yours is turned off and you want it on, here’s how.

How to Enable File Transfer

What’s the fastest way to enable Skype for Business file transfer is…use a PowerShell cmdlet! Specifically, this one: Set-CsFileTransferFilterConfiguration – TechNet

Conferencing Policy OptionsOnce enabled, you can customize file transfer options through PowerShell, or through the Control Panel. I like the Control Panel myself.

File transfer in Skype Meetings is enabled by default, as part of the Conferencing Policy with the Set-CsConferencingPolicy cmdlet. If you want to turn it off, run the cmdlet with the “-EnableFileTransfer $False” parameter.
Set-CsConferencingPolicy – TechNet

Going back to IM file transfers, the main option you have in the Control Panel is whether to block all files (essentially disabling file transfer) or block specific file types. Predictably, you find this option under “IM and Presence” in Skype for Business Server.

Skype for Business won’t let you send certain file types, due to malware risk. Here’s the full list of files Skype for Business (Server and Online) blocks:

.ade, .adp, .app, .asp, .bas, .bat, .cer, .chm, .cmd, .com, .cpl, .crt, .csh, .exe, .fxp, .grp, .hlp, .hta, .inf, .ins, .isp, .its, .js, .jse, .ksh, .lnk, .mad, .maf, .mag, .mam, .maq, .mar, .mas, .mat, .mau, .mav, .maw, .mda, .mdb, .mde, .mdt, .mdw, .mdz, .msc, .msi, .msp, .mst, .ocx, .ops, .pcd, .pif, .pl, .pnp, .prf, .prg, .pst, .reg, .scf, .scr, .sct, .shb, .shs, .tmp, .url, .vb, .vbe, .vbs, .vsd, .vsmacros, .vss, .vst, .vsw, .ws, .wsc, .wsf, .wsh

IM File Transfer Options

Note the bolded examples. Nobody can send .exe files? That’s because they’re blocked by default! (Don’t try to ZIP it up either; Skype will see into the ZIP and refuse to send.)

Once file transfer is enabled and blocked file types are set, you’ll need to make sure the appropriate ports are open on the firewall. Standard configurations will open the ports necessary (but it’s always good to test!).

The default ports used by Skype for Business file transfers are:
(Server)
1024-65535 TCP
6891-6901 TCP

(Online)
443 TCP [Destination]
50040 – 50059 UDP and TCP [Source]
443 TCP, 50000 – 59999 TCP [Destination]
Allow:
*.infra.lync.com
*.online.lync.com
*.resources.lync.com
Office 365 URLs and IP Address Ranges

When to Turn File Transfer Off: When Compliance Demands

Surprisingly, there IS a situation where you would want to turn File Transfer off, and leave it off. When you have to maintain a regulatory compliance standard.

In Skype for Business Online, file transfers within Instant Messaging are considered a “non-archived feature.” That means the feature isn’t captured when you have an In-Place Hold set up in Exchange. Thus the data you would send via file transfer doesn’t get recorded…which can jeopardize compliance.

(Shared OneNote pages and PowerPoint annotations are also non-archived features.)

This option is controlled at the user level. In the Skype for Business Admin Center, under Users, you’ll find the option for turning off non-archived features. You’re supposed to “select this option if you’re legally required to preserve electronically stored information.”

Configure Settings for Individual Users – Office 365 Support

A more detailed explanation for this setting is at: Demystifying a User Compliance setting in Skype for Business Online – Curtis J..

File Transfers Take Some Consideration, But Carry High Value to Users

In most deployments, file transfer is “just another part of the process.” Given the pieces involved though, file transfers do merit a little extra thought during setup. Mostly to make sure they function correctly for all users. Because when they don’t, it doesn’t matter if it’s 50 users or one…you’ll hear about it!

The next post may be a little delayed. I have a special review in the works…a popular third-party app got an upgrade, and I get to test it out!

What’s your File Transfer story? Did you run into a strange problem, or need to change its default setup? Please comment or email. And join us again next time!

What’s Involved in a Skype for Business File Transfer
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