You have to set some environment variables, such as LANG, LC_CTYPE, LC_MESSAGES to your local language. Usually LANG (or LC_ALL) is sufficient. Note that modern distributions and operating systems do this for you automatically.

Under UNIX, if you need to set e.g. the LANG environment variable manually, execute the following command (using sh or related shell):

export LANG=value

Replace value with a valid ISO language code (e.g. en_GB for British English).

If you intend to set the displayed language manually under Windows, you can do so by creating the LANG environment variable with a valid ISO language code value under Control Panel → System → Advanced+Environment Variables.

Also see the question regarding environment variables that have effect on Sylpheed.

Yes. In Configuration → Common preferences..., under the Display tab.

In Configuration → Common preferences... under the Display tab, you can press the button Set display item of summary.... That pops up a screen with all the options you can show or leave out of the message list.

Under UNIX, you can directly edit the appropriate hidden setting stored in the $HOME/.sylpheed-2.0/sylpheedrc configuration file by changing the setting value to 0, or 1, respectively (default is on, i.e. 1):

enable_rules_hint=0

The above does not work under Windows, however, so you have to edit the C:\Program Files\Sylpheed\share\themes\MS-Windows\gtk-2.0\gtkrc file and set the following setting to 1, or 0, respectively (default is off under Windows, i.e. 0):

GtkTreeView::allow-rules = 1

You can. In Configuration → Common preferences, under the Details and External commands tabs, you can define your editor of choice. Remember, if you want to use a command line editor like vi or emacs, to write the name of the shell (term, term, rxvt) with the -e parameter in front of the editor. E.g.: rxvt -e vi %s.

Also, make sure that you have checked Automatically launch the external editor in Common preferences → Compose → Editor, if you want the editor of your choice to be launched every time you begin composing a message.

You can set the GTK+ font by $HOME/.gtkrc-2.0, or $HOME/.gtkrc-2.0.mine, (which is included by $HOME/.gtkrc-2.0). For example:

style "default" {
       font = "-adobe-helvetica-medium-r-normal--12-*-*-*-*-*-iso8859-1 "
}
widget_class "*" style "default"

In Configuration → Common preferences..., there is a checkbox Save sent message to outbox. Uncheck it, and it's solved.

Unlike Sylpheed 1.x, Sylpheed 2.x and 3.x doesn't allow direct modification of the menu shortcuts by default. Nevertheless, you can use the following methods to configure them:

After that, the key binding change itself is very simple. Suppose you want to assign a shortcut key to a function, e.g. sending all mail out should start when you press Ctrl+Y. Click the Message menu and move the mouse over Send all messages. Now you press Ctrl+Y. Immediately the menu text is updated and the function is in place. Please note that a previous function that Ctrl+Y was assigned to, will no longer have a shortcut key. If you want to remove the key binding, do the same thing, but press the Delete key on the menu item. Then the key binding is removed.

Also see Configuration → Common preferences... → Details → Interface+Set key bindings... where you are able to reset the Default key bindings, or use other predefined key bindings.

Of course! Not all windows, but by pressing Escape, you can close the address book, the window of viewing a mail source (View → Message source), the window of viewing the headers, and several others. Just give it a try and you will find all of them.

As of 0.4.65 you can. The options are:

     %y = year in numbers     %m = month in number
     %d = day in numbers      %c = date/time for locale
     %A = full weekday name   %a = short month name
     %B = full month name     %b = short month name
     %H = hours in 24-clock   %I = hours in 12-clock

For more information, go to the Configuration → Common preferences → Display → General and choose the ... labeled button. For more options, see man 3 strftime.

You need to enable displaying of the header pane in the general preferences.

You may not have compiled in Compface support. See the appropriate question in the Installation and Configuration section.

You need to double click the URL. Also, check that you have configured your web browser correctly in Configuration → Common preferences... → Details → External commands.

When you try to launch a helper application, like an image viewer, with an attachment that has spaces in the name, put quotes around the %s parameter. Example: gedit '%s'

Under Windows, if you have created e.g. a simple batch file to echo a line to be included in your dynamic signature, you need to execute the command (specified under Account preferences → Compose → Signature+Command output) using either forward slashes or double backslashes for paths, for example:

cmd /c 'c:\\signature.bat'

Note that it is also recommended to enclose paths with single quotes, as is illustrated above.

Open Configuration → Preferences for current account... → Compose. There you can check the Bcc checkbox and optionally enter an email address.

Go to View → Customize toolbar... and select items from the Available items list to be displayed on the toolbar. You can modify the order by using the Up or Down button. The customization dialog also offers you to revert your modifications to default.

Go to Configuration → Common preferences... → Details → Interface, and select Always open messages in summary when selected.

Very often, when you are subscribed to a mailing list, you will store each message from that list in a folder dedicated to that list. Depending on remote software solution and configuration, mailing lists tend to include some words in the Subject header to identify the messages, optionally accompanied with a message number, for instance [sylpheed:33101]. These additions do not provide useful info if you have organized your folders as described, but Sylpheed allows you to disable displaying the additions in summary, and/or, if you wish, delete the additions on reply.

To do that, right-click on a folder from the folder tree, and select Properties... In the Folder properties dialog, check Don't display [...] or (...) at the beginning of subject in summary, or Delete [...] or (...) at the beginning of subject on reply, respectively.