Is your Office 365 running slow at random times? Does it seem to happen at work but be fine from home (or some other location)? Here is a short check list to help diagnose the problem.

Where is your Office 365 Tenant located?

Make sure your tenant is hosted in a location that makes sense. For us New Zealanders, the nearest location is Australia. Check the Office 365 Datacenter map.

Are you behind a Firewall or Proxy Server?

All Office 365 services use SSL. Firewalls and Proxy server with SSL Packet Inspection enabled can be a source of latency, especially if they are under a heavy load. Does turning off packet inspection improve performance? Does the Firewall’s console show high memory or CPU usage? This article ‘Should you use SSL Inspection’ by Forinet is a good read and applies to other vendors too.

Check your international bandwidth

In New Zealand some ISP’s limit the amount of international bandwidth allocated to each customer. If you have a large number of users, this could be a bottleneck. Talk to your ISP about the bandwidth allocation. Some may also have Office 365 specific plans.

Express Route is another technology that can improve performance for Azure and Office 365. See Microsoft’s Express Route partners and peering locations document. Talk to your ISP about Express Route.

Are you connecting across a WAN to your company internet connection?

If you are working from a branch office, then your internet traffic may be passing over a WAN link before getting to the internet. How much bandwidth do you have and are you sharing it with other traffic? Are you slowing down when someone prints a big file?

Other things to check

• Network switches on your local LAN. Look for packet loss, latency and retry errors
• Wireless network. Is the issue related to your WiFi only?
• Your PC (or Mac). Is the problem specific to one device?
• Run a speed test on your internet connection.
• Are you over your data cap?

For a details example of how to troubleshoot Office 365 performance, read this article from Microsoft Premier Support.

There are other reasons Office 365 might be running slow, but in my experience most issues relate to the environment users are in. Try to eliminate the easiest things first.