p.s. If the answer to my main question is NO, could someone suggest a better way for me to accomplish my goal of keeping "TBird on PC" as my main, central client (where I move a lot of messages from inbox to local folders) but also enabling me to use my smartphone to read, delete, and send messages from the same account/server?

The first real requirement is stop using POP and start using IMAP.

Why you ask. Because IMAP will synchronize Thunderbird and your smart phone with your gmail account.

Now you set the archive folder of your gmail account to local folders in Thunderbird. So when you want to move a message from the current active synchronized set, you archive it, and it is moved to local folders. Thus removing the item from Gmails IMAP synchronization.

GMail itself usually uses All Mail as an archive, and you will need to make setting changes on gmails site to actually remove mail when it is deleted, (moved out of gmail) and not archive to all mail. Otherwise you will get an offline store, but will also end up with copies in All Mail on Googles server. Not what you want from the sounds of it.

Thanks for the suggestion. I will consider changing to IMAP. First though I should mention the main server I am dealing with is Comcast not Google/gmail, in case that affects how folks respond.

Is it correct that you are answering my main question 'no'? Or are you just saying that you think using IMAP would be smarter, even if the answer to my main question is 'yes'?

Also, if you can point me to specific instructions for converting my existing pop configuration/account to IMAP that would be very helpful. I guess maybe I shouldn't even assume it will be possible with Comcast?

Appreciate any additional advice you may have.

if you can point me to specific instructions for converting my existing pop configuration/account to IMAP that would be very helpful.

http://kb.mozillazine.org/Convert_a_POP_account_to_a_IMAP_account

Your original question, I skimmed over as what you have done will work, sort of but it will be clumsy and will not really give you a satisfactory result. Sure all mail will go to both devices, but it will be unread and when you delete it you will have to do it twice. You are setting up two completely separate and isolated silos of mail.

IMAP will see you doing things once.

Archive in Thunderbird as I suggested will see the mail disappear from the phone and the comcast server. Conversly dleting on the phone will delete on Thunderbird so it does have potential for an oops.

Using comcast IMAP is actually easier that using Googles, because you do not have to fight with Googles "newer delete anything" policy. The only thing to remember is I think Comcast automatically age mail and empty the trash on a regular basis. Like deleting trash and mails over a month old once a month. what their retention policies are you would really need to check with them.

Ok thank you christ1 for the instructions to create a new account that is IMAP instead of POP. Seems a little more involved than I was hoping, but so be it.

Matt your input is much appreciated.

I guess I can start to wrap up my investigation with some initial conclusions.

1. The answer to the main question I have posted (the title of the post) is NO. I can't just change the configuration of my existing POP account so that it will delete from server any message that I move from inbox to a local folder.

2. If I want to keep using Thunderbird as my central client tool, including my place to store messages-- but also be able to view and delete messages from my smartphone-- I should use an IMAP type Thunderbird account.

Please correct any of that if needed. I'll then close out the question as solved.

It turns out that I have a gmail account in addition to my comcast account-- the gmail account is set up only to forward to the comcast account; I don't use Thunderbird with the gmail account. For a while, I have been meaning to transition away from the comcast account to the gmail account, and ultimately close down the comcast account. The trouble I'm having with being able to use the smartphone and TBird on the same account (which precipitated the question I have posted here) may just be the nudge that I need, to go ahead and make the jump. I think I will configure a new IMAP Thunderbird account to point at my gmail account, and begin the process of changing my email address of record to be the gmail one so I can eventually ignore and shut down the comcast account. If you have any additional tips or advice for me, embarking on that process, please send them.

you have gmail forwarding to comcast. Now emove that and set gmail to collect from Comcast.

Set your phone and Thunderbird to use Gmail. Your conversion is over, until such time as you move away from comcast as an internet service provider.

OK. I finally got back to dealing with this. Took me a while, but problem solved (as far as I can tell). Input from Matt and christ1 was very helpful. (Good suggestion Matt, to just reverse my forwarding--that is a part of what I did.) I give here a recap of what I learned and what I did.

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First of all, I conclude that the answer to the title question is NO.

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Bottom line comparison between starting point and ending point:

STARTING OUT

• Comcast email account is the account I use most

• TBird has a POP account for Comcast email; TBird is used to store messages locally on PC and not server, which I want to continue

• Android gmail app on smartphone points to Comcast account

• Problem is that messages moved from TBird inbox to TBird storage folder are not removed from Android gmail app-- requiring "double-delete" (i.e. move to storage folder in TBird AND delete in Android)

• Meanwhile, gmail account forwards to Comcast account (storing nothing on server); no TBird account for gmail yet but want to transition away from using Comcast account in favor of gmail account

NOW (ENDING POINT AFTER CHANGES/FIX)

• Gmail is most-used account

• Comcast account now only forwards to gmail account (saves nothing on its server); can eventually be retired

• TBird set up with new IMAP account pointing to gmail account

• Android app set to point to gmail account also

• Local storage still within TBird and not on server, because all storage folders are in Local Folders in TBird

• Now, changes made once by EITHER Android or TBird (message deletion; AND moving message to Local Folders in TBird) are reflected at gmail server and therefore in both Android and TBird-- hurrah!

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First I read as much about IMAP and POP as I could. Having used POP only, and never really having thought twice about it, it was a bit of a challenge to learn them both and then start thinking in terms of IMAP, but I'm pretty sure I do get it now.

A key point for me to learn was how TBird works, with respect to the difference between folders inside an account vs folders inside Local Folders. For a POP account they are the same, in that neither is attempted to be mirrored or synced with the server. But for IMAP, they are very different-- the Local Folders being the only place that is NOT being synced.

My locally stored folders are many and large, and I had been keeping them inside my account folders in TBird. (I had also been incorrectly referring to them as "local folders"-- based mostly on how they function, see next comments-- even though they were not inside Local Folders.) Because I had only been using POP, this meant they were not mirrored on the server.

Remember, my goal was to continue to have all or most of my stored folders in TBird local to my PC, and also not on the server. So after a quick test I confirmed that once I started using IMAP it meant I couldn't keep them where I had been keeping them before, inside the account's folders. Instead I had to move them to Local Folders.

So that was the first thing I did. Moved all my stored folders from inside my TBird account to Local Folders.

(BTW, this was not exactly a smooth experience. TBird seemed to only let me move one or two big folders before no longer being responsive. I would have to close out and open back up, to resume the effort. Eventually I think I prevailed, though. I did plenty of compacting along the way. I wish I understood why TBird was so cantankerous about this...)

Next I of course discontinued the forwarding that was happening from my gmail account to my Comcast account.

Then, I basically followed the instructions christ1 pointed me to, at http://kb.mozillazine.org/Convert_a_POP_account_to_a_IMAP_account , to create a new TBird IMAP account pointed at my gmail account.

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Meanwhile there are three different sets of settings I had to get familiar with:

1. The settings inside Thunderbird.

I accepted most of the defaults for a new IMAP account. Here are some that I paid close attention to:

a. I chose "on delete, move to trash" and "on exit, empty trash". It seems this is the only way to ever have a hope that a message will actually be deleted from the server. (I am amazed at how gmail defaults to just slurping up and archiving every message in the universe and not actually deleting them, i.e. instead of just labeling them deleted but keeping them, even if you tell it to!)

b. I disabled all archiving. Remember, my goal is to keep my messages locally on my PC but not on the server.

c. Under Copies and Folders I did not save sent messages anywhere except in Sent on the server. More on Sent messages below.

2. The settings for my gmail account on the google server.

The only tab (among the 10 available!) that really mattered here, for purposes of this discussion, was POP/IMAP Download. Under that tab, the POP settings don't matter any more so I disabled POP. For IMAP I chose enable of course, then "auto-expunge on" (to avoid sync trouble between Android and TBird).

At first I thought I was going to need to learn the details of gmail's "labels" system but thankfully has so far been unnecessary. Happy to keep that under the hood, so to speak, for now.

3. The settings in the Android app on my smartphone.

The options here are simpler. The default action is to delete (not archive). And gmail sync is on.

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So the next step was to apply those settings in TBird (#1), then at the gmail server using the web interface (#2). Finally I created an account with the Android app (#3), for the gmail account (and deleted the one for the comcast account). And very last, I set the comcast server to forward to the gmail account.

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Now, about sent mail. The Sent mail and Inbox folders are the only ones on the server that are "live" (i.e. sync'd with both TBird and the Android app). Messages I send (from either TBird or the Android app) will continue to accumulate there on the server, as well as within TBird, but I only want them in the latter place (my local disk). So to accomplish this, once a year I will, within Thunderbird, move the prior years' worth of sent messages from Sent to my storage folder (in Local Folders). This way there will be no growing accumulation of messages on the server-- only my PC.

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Thanks for the help folks. This was rather more tedious than I thought but I had to dig in and get it correct, because I had a similar situation for work accounts as well, and needed a good fix. Hopefully my detailed explanation can be use to others who may have similar situations.