Are you sure you have set them up as IMAP? it sounds like pop, not IMAP.

what mail provider are you using?

When I look at the Server settings it definitely says IMAP Mail Server and the port is set to 993.

The IMAP server is the in-house Centos 7 server with dovecot.

Please add the troubleshooting information to your post To find the Troubleshooting information:

• Open Help (or click on three-line-icon and select Help)
• Choose Troubleshooting Information
• Use the button Copy to clipboard to select all. Do not check box "Include account names"!
• Paste this in your post.

Here is the info.

The account in question is account7.

Cheers and thanks, Stephen

 Application Basics

   Name: Thunderbird
   Version: 45.0
   User Agent: Mozilla/5.0 (X11; Linux x86_64; rv:45.0) Gecko/20100101 Thunderbird/45.0
   Profile Directory: Open Directory

             (Local drive)
   Application Build ID: 20160418143821
   Enabled Plugins: about:plugins
   Build Configuration: about:buildconfig
   Memory Use: about:memory

 Mail and News Accounts
   account2:
     INCOMING: account2, , (none) Local Folders, plain, passwordCleartext

   account5:
     INCOMING: account5, , (imap) mustang.sdc.com.au:143, plain, passwordCleartext
     OUTGOING: , localhost:587, plain, none, true

   account6:
     INCOMING: account6, , (imap) sdc.com.au:143, plain, passwordCleartext
     OUTGOING: , sdc.com.au:587, alwaysSTARTTLS, passwordCleartext, true

   account7:
     INCOMING: account7, , (imap) www.benparts.com.au:993, SSL, passwordCleartext
     OUTGOING: , www.benparts.com.au:25, plain, none, true

 Crash Reports

 Extensions
   Addressbooks Synchronizer, 1.1.4, true, addressbookssync@ggbs.de
   Lightning, 4.7, true, {e2fda1a4-762b-4020-b5ad-a41df1933103}
   LookOut, 1.2.13, true, lookout@aron.rubin
   Sieve, 0.2.3h, true, sieve@mozdev.org

 Important Modified Preferences

   Name: Value

     accessibility.typeaheadfind.flashBar: 0
     browser.cache.disk.capacity: 358400
     browser.cache.disk.filesystem_reported: 1
     browser.cache.disk.smart_size_cached_value: 358400
     browser.cache.disk.smart_size.first_run: false
     browser.cache.disk.smart_size.use_old_max: false
     extensions.lastAppVersion: 45.0
     mail.openMessageBehavior.version: 1
     mailnews.database.global.datastore.id: 4069a2cb-6cfc-422e-97d5-01718c8a342
     network.cookie.prefsMigrated: true
     network.predictor.cleaned-up: true
     places.database.lastMaintenance: 1470990121
     places.history.expiration.transient_current_max_pages: 95270
     plugin.importedState: true
     plugin.soname.list: libXt.so:libXext.so
     print.print_bgcolor: false
     print.print_bgimages: false
     print.print_duplex: 0
     print.print_evenpages: true
     print.print_in_color: true
     print.print_margin_bottom: 0.5
     print.print_margin_left: 0.5
     print.print_margin_right: 0.5
     print.print_margin_top: 0.5
     print.print_oddpages: true
     print.print_orientation: 1
     print.print_page_delay: 50
     print.print_paper_data: 0
     print.print_paper_height: 11.69
     print.print_paper_name: iso_a4
     print.print_paper_size_type: 1
     print.print_paper_size_unit: 0
     print.print_paper_width: 8.27
     print.print_scaling: 1.00
     print.print_shrink_to_fit: true
     print.print_to_file: false
     print.print_unwriteable_margin_bottom: 20
     print.print_unwriteable_margin_left: 25
     print.print_unwriteable_margin_right: 25
     print.print_unwriteable_margin_top: 20
     print.tmp.printerfeatures.Lexmark.can_change_colorspace: false
     print.tmp.printerfeatures.Lexmark.can_change_downloadfonts: false
     print.tmp.printerfeatures.Lexmark.can_change_jobtitle: false
     print.tmp.printerfeatures.Lexmark.can_change_num_copies: true
     print.tmp.printerfeatures.Lexmark.can_change_orientation: true
     print.tmp.printerfeatures.Lexmark.can_change_paper_size: true
     print.tmp.printerfeatures.Lexmark.can_change_plex: false
     print.tmp.printerfeatures.Lexmark.can_change_printincolor: true
     print.tmp.printerfeatures.Lexmark.can_change_resolution: false
     print.tmp.printerfeatures.Lexmark.can_change_spoolercommand: false
     print.tmp.printerfeatures.Lexmark.colorspace.0.name: default
     print.tmp.printerfeatures.Lexmark.colorspace.count: 1
     print.tmp.printerfeatures.Lexmark.has_special_printerfeatures: true
     print.tmp.printerfeatures.Lexmark.orientation.0.name: portrait
     print.tmp.printerfeatures.Lexmark.orientation.1.name: landscape
     print.tmp.printerfeatures.Lexmark.orientation.count: 2
     print.tmp.printerfeatures.Lexmark.paper.0.height_mm: 210
     print.tmp.printerfeatures.Lexmark.paper.0.is_inch: false
     print.tmp.printerfeatures.Lexmark.paper.0.name: A5
     print.tmp.printerfeatures.Lexmark.paper.0.width_mm: 148
     print.tmp.printerfeatures.Lexmark.paper.1.height_mm: 297
     print.tmp.printerfeatures.Lexmark.paper.1.is_inch: false
     print.tmp.printerfeatures.Lexmark.paper.1.name: A4
     print.tmp.printerfeatures.Lexmark.paper.1.width_mm: 210
     print.tmp.printerfeatures.Lexmark.paper.2.height_mm: 420
     print.tmp.printerfeatures.Lexmark.paper.2.is_inch: false
     print.tmp.printerfeatures.Lexmark.paper.2.name: A3
     print.tmp.printerfeatures.Lexmark.paper.2.width_mm: 297
     print.tmp.printerfeatures.Lexmark.paper.3.height_mm: 279
     print.tmp.printerfeatures.Lexmark.paper.3.is_inch: true
     print.tmp.printerfeatures.Lexmark.paper.3.name: Letter
     print.tmp.printerfeatures.Lexmark.paper.3.width_mm: 215
     print.tmp.printerfeatures.Lexmark.paper.4.height_mm: 355
     print.tmp.printerfeatures.Lexmark.paper.4.is_inch: true
     print.tmp.printerfeatures.Lexmark.paper.4.name: Legal
     print.tmp.printerfeatures.Lexmark.paper.4.width_mm: 215
     print.tmp.printerfeatures.Lexmark.paper.5.height_mm: 431
     print.tmp.printerfeatures.Lexmark.paper.5.is_inch: true
     print.tmp.printerfeatures.Lexmark.paper.5.name: Tabloid
     print.tmp.printerfeatures.Lexmark.paper.5.width_mm: 279
     print.tmp.printerfeatures.Lexmark.paper.6.height_mm: 254
     print.tmp.printerfeatures.Lexmark.paper.6.is_inch: true
     print.tmp.printerfeatures.Lexmark.paper.6.name: Executive
     print.tmp.printerfeatures.Lexmark.paper.6.width_mm: 190
     print.tmp.printerfeatures.Lexmark.paper.count: 7
     print.tmp.printerfeatures.Lexmark.plex.0.name: default
     print.tmp.printerfeatures.Lexmark.plex.count: 1
     print.tmp.printerfeatures.Lexmark.resolution.0.name: default
     print.tmp.printerfeatures.Lexmark.resolution.count: 1
     print.tmp.printerfeatures.Lexmark.supports_colorspace_change: false
     print.tmp.printerfeatures.Lexmark.supports_downloadfonts_change: false
     print.tmp.printerfeatures.Lexmark.supports_jobtitle_change: false
     print.tmp.printerfeatures.Lexmark.supports_orientation_change: true
     print.tmp.printerfeatures.Lexmark.supports_paper_size_change: true
     print.tmp.printerfeatures.Lexmark.supports_plex_change: false
     print.tmp.printerfeatures.Lexmark.supports_printincolor_change: true
     print.tmp.printerfeatures.Lexmark.supports_resolution_change: false
     print.tmp.printerfeatures.Lexmark.supports_spoolercommand_change: false

 Graphics

     Adapter Description: Intel Open Source Technology Center -- Mesa DRI Intel(R) Haswell
     Vendor ID: Intel Open Source Technology Center
     Device ID: Mesa DRI Intel(R) Haswell
     Driver Version: 3.0 Mesa 10.6.9 (git-8957b69)
     WebGL Renderer: Intel Open Source Technology Center -- Mesa DRI Intel(R) Haswell  -- 3.0 Mesa 10.6.9 (git-8957b69)
     GPU Accelerated Windows: 0

     AzureCanvasBackend: cairo
     AzureSkiaAccelerated: 0
     AzureFallbackCanvasBackend: none
     AzureContentBackend: cairo
     CairoUseXRender: 1

 JavaScript

 Incremental GC: 1

 Accessibility

   Activated: 0
   Prevent Accessibility: 0

 Library Versions

     Expected minimum version
     Version in use

     NSPR
     4.12
     4.12

     NSS
     3.23 Basic ECC
     3.23 Extended ECC

     NSS Util
     3.23
     3.23

     NSS SSL
     3.23 Basic ECC
     3.23 Extended ECC

     NSS S/MIME
     3.23 Basic ECC
     3.23 Extended ECC

I should have mentioned that the other accounts work as expected suggesting that the issue may be at the www.benparts server.

Another update. It now seems that I am the only user with this issue. Other users see all folders with TB as well as web-based EPL and Android K9.

I guess this means that it is my TB setup that is off.

Not necessarily. I would say the jury was still out.

But I would try disabling the sieve add-on and see if that helps. I could be breaking some other part of the IMAP experience. Especially as the add-on does not appear to have had any real updates in a couple of years.

The problem existed before I installed sieve (yesterday) and remains if I now disable it. Normally, the Inbox icon has an expand/collapse chevron. This account does not.

I just deleted the account and recreated it and the problem has gone away. I'm afraid I have no idea what might have changed.

Thanks for your support. Stephen

Imap accounts get their folder names from the server. no chevron indicates that no synchronization occurred. So I guess there was an error in the account setup, like a typo in your user name.

It can't have been the user name as incoming email was visible so the correct Inbox was being retrieved so the correct user Maildir was found. But, as you say, it must have been some error in the original account setup. Thankfully, all is now good. Thanks again, Stephen