How to fix slow IMAP syncing issues in Outlook (Mac OS)

Maybe your computer is overloaded by a "demanding" program, or maybe your antivirus was scanning your computer in the background, but it got stuck. Turn your computer off and turn it back on after a minute or two and check if syncing to Outlook is faster.

In order for outlook to be able to sync emails faster, it requires a strong and stable Internet connection. If your Internet connection is not strong enough, the syncing process will be slower. Ensure that your Internet connection is strong and check if the IMAP is slow again.

Tips to improve the Internet connection include:

• If you are far away from a router, get closer to it;
• Buy a signal booster;
• If the router is weak, buy a stronger one;
• Connect your computer directly to the router, using an Ethernet cable;
• and other tips available in the slow Internet guide.

The more emails you are trying to sync, the slower the sync becomes. Additionally, if emails contain attachments, i.e. if the emails are richer with photos, special effects, etc. they are greater in size, which would take additional time to sync. Make sure to delete old emails you don't need, to make syncing faster.

Note: To achieve this purpose, you may also activate the auto-archive option Outlook has, by following the steps below:

1. Click on File and then on Options;  
   

   

2. Click on Advanced;
3. Click on the AutoArchive Settings button under AutoArchive;
   

   

4. Tick the checkbox next to Run AutoArchive and enter your preferred archiving frequency;
   

   
   
   

5. Click on the OK button to save the changes.

Disable automatic syncing of sub-folders, because it can help with speeding up syncing of emails in Outlook. To disable automatic syncing of sub-folders, feel free to follow the steps below:

1. Click on the Send / Receive tab;
2. Click on Send/Receive Groups;
3. Click on Define Send/Receive Groups;
4. In the next window, click on Edit...
5. Untick the checkbox next to Get folder unread count for subscribed folders;
6. Tick the checkbox next to Receive mail items;
7. Click on Use the custom behavior defined below;
8. Under Folder Options, expand the Inbox folder and untick all the sub-folders.
9. Save the changes.
   
   

By doing the changes above, only the inbox folder will be synced automatically.

Note: According to users who had the same issue, enabling the Download complete items including attachments for subscribed folders option, the purpose of which is to download the whole emails with attachments included, helped them fix this issue, since Outlook doesn't have to spend time separating attachments from emails.

Add-Ins installed to Outlook can make syncing, and Outlook in general, slower, as Outlook will also need to allocate resources to them, too. Disable all the Add-Ins you don't need and leave only the ones you frequently use. To disable Add-Ins, follow the steps below:

1. Go to File > Options > Add-Ins, or File > Manage Add-ins/Manage Apps, depending on the Outlook version
2. Select the Add-Ins you wish to disable, or untick the checkboxes next to them;
3. Restart Outlook.
   
   

Note: Outlook 2016 can quickly locate the Add-ins that might be slowing down Outlook. To find them, follow the steps below:

1. Go to File and click on Info;
2. Scroll down on the right pane and click on the Manage COM Add-ins;
3. Disable the add-ins that may appear, by unticking the checkbox in front of it, and clicking on the OK button;
   
4. Restart Outlook.

If you are subscribed to many RSS feeds, it may slow Outlook down. The best course of action, in this case, would be to disable them in the Advanced settings of Outlook.

Installing the latest Outlook updates is a must, if you want to make the most of it, and to resolve various issues, including this one. To check for, and install updates, to Outlook 2010 and newer versions, follow the steps below:

1. Click on File and select Office Account;
2. Click on the Update Options button;
3. Click on Update Now.
   

   
   
   

If you use an older version of Outlook, older than Office 2010, follow the steps below:

1. Open the Outlook app;
2. Click on Help and then on Check for Updates;
3. Click on Automatically Download and Install, under How would you like updates to be installed?
4. Click on Check for Updates.
   
   

Note: You may also update Outlook via App Store, by opening the App Store app, clicking on Updates and then on the Update button next to Outlook.

All the email related data are stored in a PST (Personal Storage Table) file. Over time, this file can grow large in size, and make Outlook syncing slower. In this case, what you can do is to compact this file, by following the steps below:

1. Click on File and on the Info tab;
2. Click on Account Settings, and select the Account Settings option;
   
   

   

3. Click on the Data files tab;
4. Select all the data you want to compact;
5. Click on Settings;
   

   

   
   
6. Click on Advanced;
7. Click on Outlook Data File settings;
8. Click on Compact Now;
   

   

9. Follow the on-screen instructions.

If you have more sub-folders, each of which has many emails, consider unsubscribing from some, if not from all of the sub-folders, so that they aren't synced every time you do a major sync. Basically, what you need to do is to right-click each of the sub-folders and select Unsubscribe. Alternatively, depending on the Outlook version, you have installed, to access the sub-folders, click on Folder > IMAP Folders > Query

Subscribe only to the Inbox, Drafts, Sent, Trash, and possibly the Junk folder. To see all the other folders, you need to untick the check box next to When displaying hierarchy in Outlook, show only subscribed folders at the bottom of the window where IMAP folders are.

Disabling hardware graphics acceleration might help you fix the IMAP issue, as the acceleration itself, if it was enabled, might be the one that have caused it in the first place. To disable hardware graphics acceleration, follow the steps below:

1. Go to File and click on Options;
2. Click on Advanced and check the checkbox next to Disable hardware graphics acceleration under Display;
3. Click on OK to save the changes.
   

   
   
   

If you use Outlook 2010:

1. Click on File and then on Options;
2. Click on Mail and select Editor Options in the right pane;
3. Click on Advanced and check the checkbox next to Disable Hardware Graphics Acceleration under Display;
4. Click on the OK button to save the changes.

Another way to improve the IMAP sync speed in Outlook is to enable the "Cached Exchange Mode" option, available if you have an Outlook account (including hotmail and live). What this option does is downloading data files (emails) from the Outlook server and caching them on your computer, so that they won't be synced over and over again.

If you use Outlook versions newer than 2010, to activate this option, follow the steps below:

1. Click on File and click on the Account Settings button;
2. Click on Account Settings;
3. Click on the email account and then on the Change button;
4. Click on the toggle next to Use Cached Exchange Mode option, located under Offline Settings.
   
   

If you use Outlook 2010, follow the steps below:

1. Click on File, click on the Account Settings button and select Account Settings...;
2. In the E-mail tab, click on an email address, and then click on Change;
3. Tick on the Use Cached Exchange Mode check box, under Microsoft Exchange server;
4. Quit and restart Outlook.
   
   

Note: The "Cached Exchange Mode" option may not be available on all Outlook versions, nor all email providers, i.e. if you were unable to find the option by following the steps above, that means that this option is not supported.