If you really mean SPAM folder you will have to look elsewhere. Thunderbird does not use a Spam folder. By default it marks it as Junk and leaves it in your Inbox. You would have to setup Junk Controls to get Thunderbird to mark it as Junk and place in a Junk folder.

It may help if you access the account from webmail and add her address to the webmail contacts so she's treated as a 'trusted sender' before messages are downloaded to TB.

Thanks for both efforts, but no luck. The "Spam" folder is for Junk - I don't know why it is called Spam. I went to webmail, but she is already among the contacts listed there.

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.

Application Basics

   Name: Thunderbird
   Version: 52.2.1
   User Agent: Mozilla/5.0 (Windows NT 10.0; WOW64; rv:52.0) Gecko/20100101 Thunderbird/52.2.1
   Profile Folder: Open Folder

             (Local drive)
   Application Build ID: 20170622064432
   Enabled Plugins: about:plugins
   Build Configuration: about:buildconfig
   Memory Use: about:memory
   Profiles: about:profiles

 Mail and News Accounts
   account1:
     INCOMING: account1, , (imap) mail.lifesci.ucsb.edu:143, alwaysSTARTTLS, passwordCleartext
     OUTGOING: , mail.lifesci.ucsb.edu:587, alwaysSTARTTLS, passwordCleartext, true

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

 Crash Reports
   https://crash-stats.mozilla.com/report/index/bp-f9ddb9b0-abbc-44ba-8091-314fb2161010 (10/9/2016)

 Extensions
   Lightning, 5.4.2.1, true, {e2fda1a4-762b-4020-b5ad-a41df1933103}

 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
     dom.apps.reset-permissions: true
     extensions.lastAppVersion: 52.2.1
     font.internaluseonly.changed: false
     font.name.monospace.el: Consolas
     font.name.monospace.x-cyrillic: Consolas
     font.name.monospace.x-unicode: Consolas
     font.name.monospace.x-western: Consolas
     font.name.sans-serif.el: Calibri
     font.name.sans-serif.x-cyrillic: Calibri
     font.name.sans-serif.x-unicode: Calibri
     font.name.sans-serif.x-western: Calibri
     font.name.serif.el: Cambria
     font.name.serif.x-cyrillic: Cambria
     font.name.serif.x-unicode: Cambria
     font.name.serif.x-western: Cambria
     font.size.fixed.el: 14
     font.size.fixed.x-cyrillic: 14
     font.size.fixed.x-unicode: 14
     font.size.fixed.x-western: 14
     font.size.variable.el: 17
     font.size.variable.x-cyrillic: 17
     font.size.variable.x-unicode: 17
     font.size.variable.x-western: 17
     gfx.crash-guard.glcontext.appVersion: 45.2.0
     gfx.crash-guard.glcontext.deviceID: 0x6810
     gfx.crash-guard.glcontext.driverVersion: 16.300.2311.0
     gfx.crash-guard.glcontext.gfx.driver-init.direct3d11-angle: true
     gfx.crash-guard.glcontext.gfx.driver-init.webgl-angle: true
     gfx.crash-guard.glcontext.gfx.driver-init.webgl-angle-force-d3d11: false
     gfx.crash-guard.glcontext.gfx.driver-init.webgl-angle-force-warp: false
     gfx.crash-guard.glcontext.gfx.driver-init.webgl-angle-try-d3d11: true
     gfx.crash-guard.status.glcontext: 2
     gfx.direct3d.last_used_feature_level_idx: 0
     mail.openMessageBehavior.version: 1
     mail.winsearch.firstRunDone: true
     mailnews.database.global.datastore.id: a196bc73-1079-4121-97ae-c6ce8c8b7c9
     media.gmp.storage.version.observed: 1
     network.cookie.cookieBehavior: 3
     network.cookie.prefsMigrated: true
     network.predictor.cleaned-up: true
     places.database.lastMaintenance: 1498438290
     places.history.expiration.transient_current_max_pages: 105008
     plugin.importedState: true
     security.sandbox.content.tempDirSuffix: {2f1c8773-e98c-4e33-b67c-094be5d9754d}

 Graphics

     GPU #1
     Description: AMD Radeon R9 200 Series
     Vendor ID: 0x1002
     Device ID: 0x6810
     RAM: 2048
     Drivers: aticfx64 aticfx64 aticfx64 amdxc64 aticfx32 aticfx32 aticfx32 amdxc32 atiumd64 atidxx64 atidxx64 atiumdag atidxx32 atidxx32 atiumdva atiumd6a atitmm64
     Driver Version: 22.19.162.4
     Driver Date: 4-24-2017

     Features
     Direct2D: false
     DirectWrite: true (10.0.15063.413)
     WebGL Renderer: Google Inc. -- ANGLE (AMD Radeon R9 200 Series Direct3D9Ex vs_3_0 ps_3_0) -- OpenGL ES 2.0 (ANGLE 2.1.0.2a250c8a0e15)

     AzureCanvasBackend: skia
     AzureCanvasAccelerated: 0
     AzureFallbackCanvasBackend: cairo
     AzureContentBackend: skia

 JavaScript

 Incremental GC: 1

 Accessibility

   Activated: 0
   Prevent Accessibility: 0

 Library Versions

     Expected minimum version
     Version in use

     NSPR
     4.13.1
     4.13.1

     NSS
     3.28.5
     3.28.5

     NSS Util
     3.28.5
     3.28.5

     NSS SSL
     3.28.5
     3.28.5

     NSS S/MIME
     3.28.5
     3.28.5

I suggest you contact whoever runs mail.lifesci.ucsb.edu and enquire about their anti-spam policy. Your description very much suggests that an external agency is mis-categorising and moving messages to the Spam folder.

Thunderbird's native system uses the word Junk and labels messages as Junk. Any reference to "Spam" generally comes from somewhere else, such as personal security software, or an anti-spam system operated by the email provider.

Please clarify; you say "the "Spam" folder is for Junk". What is your justification for this statement? Did you create this folder? Did you rename the Junk folder? Do you not also have a "Junk" folder? And do the messages from your wife which appear in the Spam folder have Thunderbird's junk icon, usually an orange flame? The absence of the Junk icon would confirm that something else is doing the moving to Spam.

Finally, look at your account settings and make sure your Personal Address Book and Collected Addresses are nominated as sources of trusted senders. Personally I wouldn't include Collected Addresses as it can become tainted by untrusted contacts.

Thank you. I think this is almost certainly right. I do not have a "Junk" folder. I don't think I named the "Spam" folder. The folder itself is marked with an orange flame, but the mail in it is not. If I mark an email in it as "not Junk", it goes back to the Inbox. If I mark an Inbox email as "Junk", it goes to the "Spam" folder, and gets an orange flame. So it seems likely that the lifesci administrators made a "Spam" folder to contain both "Junk" (defined by Thunderbird or me) and "Spam" (defined by them). Thanks so much for figuring this out and clearing it up.

I don't know why when I receive emails that are stated as junk or spam and I choose the option 'Not Spam or Junk" the software doesn't automatically update those emails so they don't appear as junk or spam in the future. Plus the sender email address is in my email address book.