#FAQFriday: 10 Causes for Outlook 2016, 2013 & 2010 Performance Issues

During email migrations and everyday Outlook usage, there are several factors that can cause Outlook to perform inefficiently or painfully slow.
This blog is designed to help IT Admins and Network Engineers to troubleshoot and resolve these types of support tickets or oversight. Here is a list of some of the most common causes for Outlook performance problems.

1.       Problems with the OST file synchronization
The OST file is the caching file that resides on a user’s workstation, hidden in the Windows profile (typical location: C:\Users\[account]\AppData\Local\Microsoft\Outlook\[account].ost).
The OST file maintains a copy of the mailbox data that it caches / syncs with the Exchange mailbox on the server. (This may be Exchange Server version 2010, 2013, 2016 or 2019, and it could be on-prem, hosted Exchange, or Exchange Online). The OST file also contains unique data to the user’s email organization and usage habits, but it serves the same purpose across platforms. The mailbox data in the OST files include user mail, folders, calendars, contacts, tasks, rules, etc., as well as connectivity information.

2.       OST file corruption
The Outlook OST files sometimes gets corrupted. This can be due to a problem with the data, or because it was stopped in the middle of a sync while the data was in transit.

3.       Cannot find Exchange Server or PST File
The Outlook profile can hang if it tries to connect to a PST file that has changed permissions or moved, or an Exchange Server that is offline, not responding, or it cannot find.
A variety of changes can cause a normal Outlook profile to suddenly not be able to connect to a server including: the Exchange Server or Exchange databases failing over, the Exchange services are stopped or hung, CAS Server connectivity, a mailbox store or Exchange Database being offline, and network connectivity issues.

Hint: if you're not sure if the problem is connectivity to an Exchange Server on-premises, you can try to ping (ping [Exchange Server name] or trace the route to the Exchange Server tracert [Exchange Server name] to the server. You can also see if you can access the user's mailbox thru Outlook on the Web (OWA) to rule out a problem with the user's account.

4.       Default Outlook profile connectivity
Sometimes during Exchange migrations or changes with the Exchange environment, an Outlook profile will default to connect to an outdated Exchange server, or a legacy Autodiscover DNS record that is no longer valid. If you see a problem like this, recreate the Outlook profile from scratch (Control Panel | Mail app).

5.       Very large default Outlook folders
Default Outlook folders include the Inbox, Sent Items, Deleted Items, Tasks, Calendar, Drafts, Sync Issues, Journal, and Junk mail. If these folders or the items in them are too large for the OST sync to handle efficiently, Outlook performance will be sluggish. If these common folders are too big, you can move some data to a sub-folder either manually or with a rule, so that the folder is less cumbersome for the Outlook sync.

Hint: Some executives and people who work with contracts, video editing, legal, and architectural blueprints tend to have very large mailboxes. You can create sub-folders for different years or general topics under the Inbox, and then create a rule to move everything with those dates to the sub-folder. For example: "2018 Mail".

6.       Very large messages with attachments in the default folders
If there are 20 MB messages or larger at the top of the inbox or sent items, the Outlook profile can be slow to connect, perform, and get hung while messages are moved around in different folders.
Hint: To decrease a mailbox or folder size quickly, sort the folder by size, detach the attachments and save them to the workstation, delete the original message, or archive them to an archive server or file vault.

7.       Too many rules
If there are a large number of rules, complicated, or conflicting  rules, Outlook may perform sluggishly.

8.       Add-ins
Outlook add-ins are often used with other Microsoft applications or third party messaging apps that integrate with Outlook. These may include email archive software, voice mail applications, calendar agents, social network connectors, Microsoft Teams, Microsoft OneNote, and other add-ins. If there is a problem with an Outlook add-in like memory leaks, add-in conflicts, or compatibility issues, Outlook can experience performance issues or hang.

9.       Email address book problems
Let’s say an administrator removes and recreates an Exchange Address Book, Outlook may be slow until it updates to the appropriate Outlook Address Book (aka Exchange GAL).

10.   Mail worms and address book viruses
Mail worms and email address book viruses are sometimes unknowingly passed around through messages, malicious macros, and attachments. Make sure each workstation has automatic updated antivirus and malware protection, and there is also antivirus protection on the mail servers and mail gateway, especially if the servers are Exchange Servers on-premises.

We hope you found this blog useful!

Stay tuned for more tips! Feel free to drop us a line, and suggest topics for future tech blogs by Email Annie.