Not sure I know what you mean. Of course I can delete emails. Even without needing to open them (marking them for deletion does not open them).

And this, maybe?
http://kb.mozillazine.org/Deleting_m..._IMAP_accounts

P.S. I used it under Windows before, now under Linux. Both work(ed) well.

I agree with Neal. One thing I've found out about MS web-based e-mail is that it attracts spam from EVERYWHERE. I only use my Hotmail account to register for spam sites and never look at it except to just delete everything every couple of months.

Random spam just doesn't come to my ISP account using Thunderbird. There's no substitute for an e-mail program that lives on your machine, not on the web, and where e-mails are downloaded to your machine, not left out there in the cloud.

Linux has a crowd of excellent e-mail programs (Thunderbird is an import from Linux, by the way). You could have a small Linux installation using WUBI so Linux is just a subdirectory in Windows. You don't have to reboot at all, just use Windows and Linux at the same time. Then you have a selection of over a dozen great locally resident e-mail programs. I'd list 'em but I'm away from home.

AFAIK, they don't actually delete. They just get archived in a hidden file that just gets bigger and bigger, wasting space on your HDD.

Not that I know of. And judging by experience with size of email-archives when migrating or saving such archives intentionally, I would not mind for the size of these files. Considering the size of modern HD, my past migration archives/backup archives, were microscopic, sub-nuclear.

But I do not tell this with guaranteed certainty. As I said, I hear your claim for the first time ever. I used the available options in Thunderbird to set things up as secure and conservative as possible, to my best knowledge. And you can have different options for every email box/adress you use with it.

Absolutely! Never forget that all e-mail lives in on-line servers. In order to securely handle them you should set up your e-mail client to download e-mails to your machine and then delete them from the server. If you want you can let them live for a week so your mobile devices don't get into a catfight.

If your computer, laptop, tablet and cell phone are all set up to download and delete from server, the first device that grabs it is the only one where you can see the e-mail. It becomes a game of "who hid the cheese." So let them live for a minimal amount of time to ensure that all devices have the same e-mails and then delete them with a schedule on the server.