What is the exact error message you get? Is the error generated by Thunderbird, or by the server?

I'd agree that with a POP account deleting messages on the server should not impact local messages. So this may just have been coincidence.

Can you post your Troubleshooting Information? Help (Alt-H) - Troubleshooting Information

I can't retreive the message, everything's gone. Inbox, from System Administrator, message something to effect you've gone over your mail size limit, you won't receive any more mail until mail has been deleted.

This was true, I assume sent by my ISP, as there were alerts there. I don't use webmail, so hadn't seen any prior messages, as nothing is sent until it's too late. My email limit is 100mb. I never had this problem until earlier this year, even tho I've been w/ this ISP for years. Tech denied any changes. If I clear my server periodically, there's no reason for me to pay for more space.

Not possible to be a coincidence twice. In both cases the minute I moved from the website, having deleted mail on server, and clicked on TB, I saw before my eyes the entire inbox disappear.

To confirm your account type, can you post your Troubleshooting Information?

Sorry, I misunderstood. here's the TS info. And I see here that it's an imap acct, but in my network setting it says it's a POP acct. Is this the problem??? The tech told me I have a POP acct. :-(

 Application Basics

   Name: Thunderbird
   Version: 24.6.0
   User Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.9; rv:24.0) Gecko/20100101 Thunderbird/24.6.0
   Profile Folder: Show in Finder
   Application Build ID: 20140610001341
   Enabled Plugins: about:plugins
   Build Configuration: about:buildconfig
   Crash Reports: about:crashes
   Memory Use: about:memory

 Mail and News Accounts
   account1:
     INCOMING: account1, , (imap) imap.tsn.cc:143, plain, passwordCleartext
     OUTGOING: smtp.tsn.cc:25, plain, passwordEncrypted, true

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

 Extensions
   Adblock Plus, 2.6.3, true, {d10d0bf8-f5b5-c8b4-a8b2-2b9879e08c5d}
   ThunderBrowse, 3.82, true, ThunderBrowse@thunderbrowse.com

 Important Modified Preferences

   Name: Value

     browser.cache.disk.capacity: 358400
     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: 24.6.0
     font.internaluseonly.changed: false
     font.name.sans-serif.x-western: Helvetica
     font.size.variable.x-western: 13
     gfx.blacklist.direct2d: 3
     gfx.blacklist.layers.direct3d9: 3
     javascript.allow.mailnews: false
     mail.openMessageBehavior.version: 1
     mail.spotlight.firstRunDone: true
     mailnews.database.global.datastore.id: f1cf07a6-d3d1-c745-a867-a36bd10298a
     network.cookie.disableCookieForMailNews: true
     network.cookie.prefsMigrated: true
     places.database.lastMaintenance: 1403070268
     places.history.expiration.transient_current_max_pages: 53688
     plugin.importedState: true
     privacy.donottrackheader.enabled: true
     security.default_personal_cert: Select Automatically

 Graphics

     Vendor ID: 0x1002
     Device ID: 0x9583
     WebGL Renderer: false
     GPU Accelerated Windows: 0

     AzureCanvasBackend: quartz
     AzureFallbackCanvasBackend: none
     AzureContentBackend: none

 JavaScript

 Incremental GC: 1

 Accessibility

   Activated: 0
   Prevent Accessibility: 0

 Library Versions

     Expected minimum version
     Version in use

     NSPR
     4.10.2
     4.10.2

     NSS
     3.15.4 Basic ECC
     3.15.4 Basic ECC

     NSS Util
     3.15.4
     3.15.4

     NSS SSL
     3.15.4 Basic ECC
     3.15.4 Basic ECC

     NSS S/MIME
     3.15.4 Basic ECC
     3.15.4 Basic ECC

It appears your account is IMAP. So what you see is exactly what's expected for IMAP. All mail is managed on the server, and what you see in Thunderbird is basically a mirror of what's on the server. With limited storage space on the server IMAP doesn't really make sense. Instead of deleting messages on the server you'd need to move them off of the server to your 'Local Folders' account. If you want to set-up a POP account instead of IMAP and you need help with that, you can ask right here.

Yes please. HELP. Thanks for solving this. I don't know how this happened. Would TB have changed these settings at an upgrade?? Doesn't seem likely...Anyway, thanks, and yes, help please.

Nope, an account can't realistically change from POP to IMAP.

(The last time I built an application that used email, I had a choice between IMAP and POP client modules. Their protocols and mail storage systems are so fundamentally different that I don't think it would be realistic to combine the two into one lump of code, so I believe that Thunderbird will have two separate "units", one each for POP and IMAP, along with another for SMTP (sending) and others for the RSS and NNTP capabilities.)

Your provider may (and probably does!) offer POP, but left to itself, when you set up an account in Thunderbird, it will opt for IMAP if it is offered. Apart from some special cases where it recognizes that both are available (gmail is an example of this) you'd have to intervene and manually enter the POP account details; usually the server name, and definitely the correct port to use.

Unfortunately, I can't see a single webpage that says definitively what the server settings need to be. They mention POP in their "paid-for email" webpage, but that doesn't mean it is the only service they offer.

http://home.tsn.cc/?s=pop

The search fails given IMAP as a search term. :-(

As Zenos already mentioned, you cannot convert an existing IMAP account into a POP account, so a new POP account needs to be created. Follow the instructions in this article. https://support.mozilla.org/en-US/kb/faq-changing-imap-pop

Note, by default POP downloads messages from the server upon accessing the account, and then removes them from the server.

You'll need to obtain the correct server settings for POP from your email provider.

Thanks to both of you. I'd never received notification of exceeding limits before this year, so I don't know when/how the change to imap happened. ...Aha, maybe this occurred when I finally successfully started using TB version 20+. I'd been stuck in a lower version (3+??), each attempt to upgrade failed. Until I got help here and created a new profile. Then it must have been set up as imap.

My ISP sent a  "rate this service" evaluation form. Unfortunately, I had to rate it down and describe how this same tech had been unable to help me identify this in our call 3 months prior, and this time around insisted it was either a coincidence or a virus, I should call a computer tech. :-(

ADDED: I've just followed the instructions to set up a new account as POP. When I get to the end of the process I'm told that there is no encryption. when I click Encrypt incoming, outgoing, it seems to not accept this prompt, so I aborted the process. Is this something that happens w/ ISP rather than in my set-up? Thanks

When I get to the end of the process I'm told that there is no encryption.

Can you be a little more specific? May be a screenshot? http://support.mozilla.org/en-US/kb/how-do-i-create-screenshot-my-problem

The instructions say:

3. Thunderbird will attempt to configure your accounts settings automatically using IMAP. Click Stop.

When I stop at this point, there is nothing I can do. No place to enter details or any choice but to press continue...or Manual Configuration. When I go to Manual Config here, and change imap to pop, I get a different warning: TB failed to find the settings for your email account.

4. Enter your account details as follows:...

5. Once these settings have been entered, click Manual Setup...

You may get an error message that says that the SMTP account already exists. Clear the message.

6. Click on Cancel to exit the Account Settings dialog. Re-open the Account Settings page and you will see that your new account has been created. Also please check your Outgoing Server (SMTP) is correct for this account"

When I Click Stop, as in #3, at that point, I'm left in the middle of the "looking for configuration" process. nothing happens. When I press continue, it continues on. That leads to the whole process that yields the un-encrypted message.

If I allow it to set-up, then go to manual Set-up I found no error message. When I then cancel and go to AcctSettings, I see no new acct.

However, when I allow the process to continue w/o Manual settings, I get the following...The screenshot won't upload, tied it twice.

It reads: Incoming Settings: pop3.tsn.cc does not use encryption Outgoing settings: smtp.tsn.cc does not use encryption. Thunderbird can allow you to get mail using the provided configurations. However you should contact your administrator or email provider regarding these improper connections. See TB FAQ for more info."

With a box to check that I understand the risks.

I can only go around in circles :-(

Thunderbird will attempt to configure your accounts settings automatically using IMAP.

In your case, IF the wizard defaults to IMAP, you want the 'Manual Configuration'.

It reads: Incoming Settings: pop3.tsn.cc does not use encryption Outgoing settings: smtp.tsn.cc does not use encryption.

Good, you got the setting for POP, which is what you want. You also get a warning, that no encryption is being used. Check with your email provider, whether they offer SSL/TLS. If not, look for a new email provider.

With a box to check that I understand the risks.

For the time being, go ahead without encryption.

Thanks. I've sent a note to my ISP, will let you know what's next. No encryption we can add on? And, how significant is it to have none?

But the manual settings only leads to the Warning: TB failed to find the settings for your email account.

No encryption means your password is always transmitted in the clear to the server. It's neither something I'd want nor tolerate from my email provider.

If the account wizard fails to automatically determine the correct account settings, run the manual setup.

https://support.mozilla.org/en-US/kb/manual-account-configuration

I keep going around in circles. that's why I'm only coming back to it every other day. :-(

Here's what the link for manual account config says:

"Enter your email account details and press Continue. Thunderbird will try to determine your account settings based on the domain portion of your email address (that is, the portion after the "@" symbol). Press the Stop button to abort the lookup, then edit the server names, port and IMAP/POP, and then press Manual Configuration to manually set up the the account. Note that it's important that you set server names, port and IMAP/POP before clicking Manual Config. (Alternatively, you can allow the lookup to gather default account details and then manually change the settings later.)"

But that must be from an earlier version. Stop at this point shows no settings, only the screen w/ name, email address, password.  :-(

UPDATE In a conversation w/ my ISP techie, I was finally able to set up a POP account. It's set up w/o encryption. I 've set it as default, tho the IMAP account is receiving my mail. She tells me they have many customers w/ POP accts, none have encryption. Only the IMAP. I'll have to do some reading about encryption, to see whether it matters. It seems I'll have to delete the IMAP account in order to actually get the POP to function. Which means possibly losing my mail again, tho there's not much to lose at this point....

Thanks for your help.

I'll have to do some reading about encryption, to see whether it matters.

It's a matter of security, and I wouldn't use email anymore without SSL/TLS.

I'll have to delete the IMAP account in order to actually get the POP to function.

No. By default POP downloads messages from the server upon accessing the account, and then removes them from the server. At the first time you access the account via POP it would get all the messages on the server. That should reflect on the IMAP account, there shouldn't be anything left there now. Your email provider's implementation may be different though, check with them. If there are messages you ultimately want to keep move them off of the (IMAP) server or copy them to your Local Folders account. Nothing should get lost in the process though.

For the future, make sure to create backups of your profile folder on a regular basis. http://kb.mozillazine.org/Thunderbird_:_FAQs_:_Backing_Up_and_Restoring

Thanks very much. I'll read the profile article. Settled on POP for now. I really appreciate your ongoing support. :-)