Fix Outlook’s IMAP “subscribed folder” synchronisation problem

We recently helped a Dublin architectural firm resolve an issue with their slow email. They had 5 Dell Optiplex computers in their office all running Windows 10 Pro. These systems were using Outlook 2016 as their email application which synced with their Blacknight email server. However, all of these systems were exhibiting the exact same problem: namely Outlook 2016 would hang after pressing “send and receive”. So, instead of emails flying into their inbox and emails flying out of their outbox – users would get a message about “synchronizing subscribed folders”. This would pop up on their screens and stubbornly linger there for around 90 seconds (sometimes longer) until the IMAP sync had completed. In a busy architectural practice this problem was, quite understandably, beginning to irritate some users. One user described the problem like rushing for an appointment only to have traffic lights continuously turn red along the route. A solution had to be found and quickly!

We performed some diagnostics. Their Virgin Media broadband speed was good both downstream (62.1 Mbps) and upstream (4.1 Mbps). The Blacknight domain, on which their website and emails were hosted, also showed no issues. Communication between client PCs and their IMAP server was stable with all ICMP requests being responded to quickly. Our suspicions were now turning to Outlook 2016. As a whole, this is a fairly reliable application, but it does have its foibles (like corrupt store folders and other quirks). In this case, we could safely rule out PST file (personal storage) corruption or Outlook user profile corruption because, while it was possible the store folders or the application itself was corrupt, it would be unlikely that all 5 users would have this problem simultaneously. Something else was at play here and we were determined to pinpoint it.

We pressed “send and receive” a few more times and each time we could see the same sequence of events happening. The blue progress bar would laboriously travel across the screen as their IMAP folders synced. Some configuration issue was causing the sync process to be extremely slow. After 1.5 hours of troubleshooting, we found the issue.

  1. Go to the Send/Receive tab in Outlook 2016
  2. Click on Send/Receive Groups dropdown arrow.
  3. Now click on Define Send/Receive groups followed by Edit.
  4. Untick box with “Get folder unread count for subscribed folders”
  5. Under Received Mail Items – tick the option for “use the custom behavior defined below”
  6. In the next dialogue box, only select “inbox” and “sent” items folders.
  7. Click “ok” and exit.

This solution was applied to every system in their office and now their Outlook is performing optimally again. To avoid this problem happening again in the future, we also configured Outlook’s “autoarchive” feature in their systems to keep their “inbox” and “sent item” folders nice and slim without being bogged down with old emails. This also helps them keep compliant with GDPR guidelines on email archiving.