Extremely slow when loading IMAP content and not all is loaded

We are moving from Thunderbird to eM Client but are facing some issues with connection performance against Zarafa running IMAP on Synology:

  • Only when actually accessing a folder, does it sync. That becomes particularly evident when using public folders and have rules that move new messages to a subfolder in the public folder hierarchy. Those messages do not appear in other eM Clients subscribing to the same public folders unless that user specifically access that folder to look for messages.
  • Receiving headers from the server takes a long time. Not critically so, but still noticeable.
  • When clicking a new message to load the content, receiving that content takes from 15 seconds upwards of 11⁄2 minutes. It does not appear to depend on the size of the content but more on how much else eM Client is doing at the time.
    Since Thunderbird works flawlessly on all three counts, I think it is fair to put the blame on eM Client and not Zarafa. Feature wise we really want to go with eM Client and thought that version 6 was the time to do it and now version 7. We really do want to switch but these issues are real show stoppers.

The mail accounts average on roughly 5GB of data at any given time in a hundred folders or so.

I have checked “Download messages for offline use” etc. to let eM Client get some asynchronous benefit. It helps a bit on old messages but not with new ones.

Big issue with slowness to download content. I also checked download messages for offline, but that does not help. I like the features, but this poor performance is a show stopper for me.