When it comes to writing emails, it turns out that I am using googlemail.com most of the time, because it has some nice features:

• Access via browser from anywhere.
• Currently 2,845 MB of space to store your emails.
• Other email addresses can be registered to use them as sender.
• Emails can be labeled.
• Searching your emails is so easy!

But:
I am missing a feature to provide a permanent BCC for outgoing emails, as I want them to be forwarded to my main POP3 account to have them offline on my PC.

I have already sent a request to Googlemail, but so far, this feature does not seem to be provided yet. What a pity that you can’t use filters on outgoing emails…

[Update from 2008-01-31]
There seems to be a workaround using this Greasemonkey script - of course, you will have to install the Greasemonkey firefox addon first.

[Update from 2008-02-05]
I just installed Greasemonkey and the gmailAutoBCC script - and it works!!!

[Update from 2008-04-23]
Google has redesigned (at least the German) Googlemail - and unfortunately, the gmailAutoBCC script is no longer working. Guys, PLEASE: make it work with the new version, quickly - I need this script! Thanks!

[Update from 2008-07-01]
Jaidev has updated the script, but there seems to be a problem with FF3 and the latest version of Greasemonkey. I got the following error message:

Script could not be installed [Exception... "Component returned failure code: 0x80520012 (NS_ERROR_FILE_NOT_FOUND) [nsIChannel.open]” nsresult: “0×80520012 (NS_ERROR_FILE_NOT_FOUND)” location: “JS frame :: chrome://greasemonkey/content/utils.js :: getContents :: line 244″ data: no]

[Update from 2008-07-03]
Following the instructions given by Chua on techiecorner.com made it happen: it now works again - thanks, guys (= Jaidev, Zebra & Chua)!