After cleaning up your mailbox by deleting old emails, emptying the Deleted Items folder, or archiving messages, you may notice that the Outlook OST file on your hard drive still shows the same size. The OST file is a local copy of your Exchange Online or Exchange Server mailbox, and Outlook does not automatically shrink … Read more
If you use Outlook with a Microsoft 365 or Exchange account, your offline OST file automatically grows as you receive and send email. When that file approaches 100 GB, Outlook may stop synchronizing, display errors, or refuse to open. This hard limit exists because the Windows Search indexer and Outlook’s database engine cannot reliably manage … Read more
When you use Outlook in Cached Exchange Mode, the default download setting keeps 12 months of email, calendar, and other items on your local machine. This can consume significant hard drive space, especially on devices with limited storage. The sync slider lets you reduce that to 1 month, meaning only the most recent 30 days … Read more
When you add a shared mailbox in Outlook, messages can take several minutes or longer to appear. This delay happens because Outlook uses Cached Exchange Mode by default. The shared mailbox must download a full copy of its items to your local machine before you can browse them. This article explains why the delay occurs … Read more
When Outlook stops syncing emails, calendars, or contacts correctly, many users assume the only fix is to delete and rebuild their mail profile. This process is time-consuming and forces you to re-enter account passwords and reconfigure settings. The problem is often caused by a corrupted local cache or a stalled synchronization state within the existing … Read more
If your Outlook Sync Issues folder is filling with conflicts, your email client is detecting two or more versions of the same item that cannot be merged automatically. This typically happens when a mailbox item is modified on the server and on your local machine at nearly the same time, or when a synchronization process … Read more
After resynchronizing your Outlook mailbox with the Exchange server or Microsoft 365, some items may end up in a hidden folder called Local Failures. This folder stores messages, calendar entries, or contacts that failed to sync during the process. The cause is typically a conflict between local cached data and server data, a corrupted item … Read more
When you open the Sync Issues folder in Outlook, you may see a subfolder named Server Failures. This folder stores error messages that Outlook generates when it fails to synchronize specific items with the Exchange server. Each item in this folder represents a failed sync attempt and is categorized by an item type such as … Read more
If you manage tasks in Outlook but want to see them in Microsoft To Do on your phone, tablet, or another computer, you need to enable the sync between the two apps. Outlook Tasks and Microsoft To Do share the same underlying Exchange task folder, but the sync is not automatic unless you turn on … Read more
When you add or update a contact in Outlook desktop, you expect it to appear in the Outlook on the web (OWA) address book. But sometimes the contact stays invisible in OWA even though it exists in the local Outlook folder. This problem is usually caused by a mismatch between the local Outlook contact folder … Read more