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Do email clients like Thunderbird download the mail to the PC they're installed on, or do they access it in real time?

If I receive mails with attachments, are they being saved on my PC even when I don't open them?

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up vote 0 down vote accepted

If you want to leave your messages on the server you should not have "For at most 14 days" checked.

Theoretically these two options (For at most 14 days / until I delete them) counter-act each other (one is saying delete, one is saying don't delete) and should really be seperated by a radio checkbox rather than tick boxes. I'm not sure how Thunderbird actually reads these options (ie, which one overrides the other) as I haven't got a copy of the source code but by what you are describing, the "For at most 14 days" checkbox is probably taking priority.

You should only tick "Until I delete them" if you want all your messages to stay on the server.

Please note that depending on how much space your email host gives you, this could rapidly run out if you do not download and delete messages from the server.

The attachments you are "downloading" are already downloaded, you're simply saving them from Thunderbird's storage to where ever you are asking it to save to.

Of course, there are other possible reasons your webmail disappeared but without more information such as how long you've been using Thunderbird, whether webmail did a maintenance purge, etc etc, it's hard to say for sure.

You can't really put the email back on the server, it's technically possible server-side but nothing you can do as a user, unless you forward all 700+ emails back to yourself. I'm not sure why you'd want them all to stay on the server anyway, if you want to save important emails or documents you should download them and save to an off-site backup like DropBox or sign up to Gmail which has so much storage you don't have to delete anything.

(Other off-site backup services and web mail services are available)

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This is (AFAIK) true for POP3, but IMAP is a lot more flexible as to whether to keep messages on the server, and does allow uploads. – Gilles Nov 21 '10 at 21:56
Just to be sure: You should only tick "Until I delete them" if you want all your messages to stay on the server would still delete them from the server, as soon as you delete them from Thunderbird. One could surely put mail back on the server when using IMAP. – Arjan Nov 21 '10 at 22:37

Put simply, yes and no. Depending on how your email is configured. There's two possible ways:

  1. POP3: In this case, it's usually set to download all your email and delete it from the server.
  2. IMAP: In this case, it really depends on the setup, but in all cases it downloads either the headers or the full email and syncs the actions to the emails with the server.

Attachments: No, those are downloaded from the server when you click on them.

Most of the time you can change how they behave but you'd have to Google it to find out how.

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thank's for the reply. My mail is pop3. on the settings tab there's an option leave messages on the server- it is checked. under that option are 2 options 1)for at most 14 days, 2)until i delete them. both of them are checked. My problem is that i have all my mail in thunderbird , but when i sign in to the webmail platform there are only a few (16 of about 700). I did not delete any mail from thunderbird or from the webmail. how can 700+ mails been lost? I also remember that all mail was also on the web platform previous week. I dont know what happened. Did thunderbird delete them? – user56378 Nov 21 '10 at 18:04
When i try to download an attachment from thunderbird from a very old message everything works fine. Does this mean that i open the attachment from my computer as far as i cant find this message from the webmail platform? Is there any way to upload my messages back to the server? – user56378 Nov 21 '10 at 18:08
Actually, attachments are generally downloaded together with the email (with POP3, I think it's the only possible behavior). – Gilles Nov 21 '10 at 21:57
@user, I guess only 16 are less than 14 days old then? (Small chance your email provider deletes messages as well, some time after they have been downloaded.) – Arjan Nov 21 '10 at 22:35
Attachments are usually downloaded when the e-mail is downloaded. So if you are using POP3 the attachment will get downloaded too. – ChrisF Nov 21 '10 at 22:41

Since you are using POP3, yes, the messages get downloaded from the server to your local computer. Attachments are technically part of the body of the message. Email was designed 40 years ago and there was no support for attachments so they found a way to 'encode' the attachments into the body and email clients 'parse out' the attachments for your convenience.

So, when you download the body of a message, you are downloading all of the attachments, even when you don't open them.

If you don't like the idea of leaving something on your computer (say you're checking your personal email account while at work) you might try a portable email client like TrulyMail Portable or Thunderbird Portable. Both allow you to run the email client from a USB drive and keep your messages in your pocket.

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