Could you please post your settings, and then we can see how they compare with what is advised by iCloud.com

Please add the troubleshooting information to your reply.

To find the Troubleshooting information:

• Open Help (or click on three-line-icon and select Help).
• Choose Troubleshooting Information.
• Clear the check box "Include account names".
• Use the button Copy to clipboard to select all and copy it to the system clipboard.
• Paste this into your post.

Application Basics

   Name: Thunderbird
   Version: 45.0
   User Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.10; rv:45.0) Gecko/20100101 Thunderbird/45.0
   Profile Folder: Show in Finder
   Application Build ID: 20160407141108
   Enabled Plugins: about:plugins
   Build Configuration: about:buildconfig
   Memory Use: about:memory

 Mail and News Accounts
   account1:
     INCOMING: account1, , (pop3) pop.verizon.net:995, SSL, passwordCleartext
     OUTGOING: , smtp.verizon.net:465, SSL, passwordCleartext, true

   account2:
     INCOMING: account2, , (none) Local Folders, plain, passwordCleartext

   account8:
     INCOMING: account8, , (pop3) pop.icloud.com:995, SSL, passwordCleartext
     OUTGOING: , icloud.com:465, SSL, passwordCleartext, true

 Crash Reports

 Extensions
   Color Folders, 1.1, true, colorfolders@fisheater.com
   Lightning, 4.7, true, {e2fda1a4-762b-4020-b5ad-a41df1933103}

 Important Modified Preferences

   Name: Value

     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
     dom.apps.reset-permissions: true
     extensions.lastAppVersion: 45.0
     font.name.sans-serif.x-western: Comic Sans MS
     font.size.variable.x-western: 12
     gfx.crash-guard.glcontext.appVersion: 45.0
     gfx.crash-guard.glcontext.deviceID: 0x0a29
     gfx.crash-guard.status.glcontext: 2
     mail.openMessageBehavior.version: 1
     mail.spotlight.firstRunDone: true
     mailnews.database.global.datastore.id: a32e6f85-21ac-0844-9db5-233f14452f0
     mailnews.database.global.views.conversation.columns: {"threadCol":{"visible":true,"ordinal":"1"},"flaggedCol":{"visible":true,"ordinal":"3"},"attachmentCol":{"visible":false…
     network.cookie.prefsMigrated: true
     network.predictor.cleaned-up: true
     places.database.lastMaintenance: 1463419125
     places.history.expiration.transient_current_max_pages: 104858
     plugin.importedState: true

 Graphics

     Vendor ID: 0x10de
     Device ID: 0x0a29
     WebGL Renderer: NVIDIA Corporation -- NVIDIA GeForce GT 330M OpenGL Engine -- 2.1 NVIDIA-10.0.35 310.90.10.05b12
     GPU Accelerated Windows: 0

     AzureCanvasBackend: skia
     AzureSkiaAccelerated: 1
     AzureFallbackCanvasBackend: none
     AzureContentBackend: quartz

 JavaScript

 Incremental GC: 1

 Accessibility

   Activated: 0
   Prevent Accessibility: 0

 Library Versions

     Expected minimum version
     Version in use

     NSPR
     4.12
     4.12

     NSS
     3.21.1 Basic ECC
     3.21.1 Basic ECC

     NSS Util
     3.21.1
     3.21.1

     NSS SSL
     3.21.1 Basic ECC
     3.21.1 Basic ECC

     NSS S/MIME
     3.21.1 Basic ECC
     3.21.1 Basic ECC

Where did you get your server settings from?

The iCloud information page gives:

incoming (IMAP): imap.mail.me.com:993 outgoing (SMTP): smtp.mail.me.com:465

Your "OUTGOING: , icloud.com:465" seems most unlikely to work.

And they say they don't support POP, so "pop.icloud.com:995" also seems unlikely to work.

I suspect you didn't (or weren't able to?) let Thunderbird find settings automatically.

I started from scratch and used the "incoming and outgoing" settings you suggested and Thunderbird failed to find the settings for my email account.

Please take a look at the attachment and see if there's anything else I may have overlooked.

Thanks

They do suggest using your full email address - have you tried that?

I have just tried signing up for an iCloud account myself. But I can't see how to get myself an iCloud email account.

I really don't like Apple stuff. This didn't do anything to change my opinion. :-(