When you click an HTML email in Outlook, the Reading Pane can take several seconds to display the content. The screen freezes or shows a blank area before the message appears. This render lag is caused by Outlook trying to download and display external images, styles, and web beacons embedded in HTML emails. This article … Read more
When Outlook is open, you may notice the process SearchIndexer.exe or Microsoft Outlook Indexer using 50% to 100% of your CPU. This happens most often when your OST file, the offline copy of your mailbox, is larger than 10 GB. The Windows Search service continuously reindexes new and changed items, and a large OST file … Read more
When you start Outlook, the status bar may display “Loading Group Policy” for 30 seconds or longer before the mailbox loads. This delay occurs because Outlook applies Group Policy settings from the Windows registry during each sign-in. The Group Policy processing can hang or take excessive time when a policy setting is misconfigured or when … Read more
When you type a name in an email’s To, Cc, or Bcc field, Outlook checks the address book to resolve the name against a contact or recipient. This lookup process can slow down if your address book is large or if Outlook has to fetch data from the server repeatedly. The Address Book Lookup Cache … Read more
When you click between folders in Outlook, a delay of several seconds or more can interrupt your workflow. This problem often occurs in Cached Exchange Mode because the view index that stores how folders display their data becomes corrupted or fragmented. This article explains why folder switching slows down and provides a direct method to … Read more
If your Outlook OST file grows too large, it can slow down performance, cause sync errors, or even prevent Outlook from opening. The OST file stores a local copy of your Exchange or Microsoft 365 mailbox data, and its size is limited only by disk space by default. This article explains how to use the … Read more
When Outlook performs a send/receive operation, it can spike disk input/output to 100 percent, making your computer unresponsive for several seconds. This typically happens when Outlook downloads large amounts of email data from the Exchange server or a large PST file. The root cause is often a combination of a full local cache, a large … Read more
When you run Outlook, it checks for new email at intervals you set in the Send/Receive groups. Calendar invitations often arrive as email messages, so they are not processed until the next scheduled send/receive cycle. This delay can cause you to miss meeting updates or new invites for several minutes. The /sniff command-line switch forces … Read more
Outlook connects to Exchange Online or on-premises Exchange servers using one of two transport protocols: MAPI over HTTP or the older RPC over HTTP. The protocol you use directly affects connection speed, reliability, and how Outlook behaves over slow or unreliable networks. This article explains the performance differences between MAPI HTTP and RPC, describes how … Read more
When Outlook connects to a slow Exchange server, the Remote Procedure Call (RPC) timeout can cause the application to disconnect or display error messages before the server finishes processing a request. The RPC timeout determines how long Outlook waits for the Exchange server to respond before it abandons the operation. This article explains how to … Read more