Users registering an account with a Geeklog-powered site will get an email containing an automatically generated password that they have to use to log into the site. The standard text of that email is as follows:

Your ''Geeklog Site'' account has been created successfully.
To be able to use it, you must login using the information below.
Please save this mail for further reference.

User Name: ''yourname''

Password: ''somepassword''

This password is generated by a randomizer. It is recommended that 
you change this password immediately. To change your password, 
log in and then click Account Information from the User Functions menu.

If you want to change the text of that message, then the simplest method is to edit Geeklog's language file, /path/to/geeklog/language/english.php (assuming English as your language), accordingly. The two sections of the above message are the strings #15 (Your account has been created successfully…) and #14 (This password is generated…), respectively, in the $LANG04 array.

Editing the language file as described above limits you to these two text sections (although they can be considerably longer than the original text, if you want to) which sometimes is just not flexible enough. Also, you'll have to make those changes again after every Geeklog update.

So, instead of using the built-in email message, you can create a simple text file that contains the text that you want to be sent to new users. That file has to be named 'welcome_email.txt' and has to be placed in Geeklog's data directory, /path/to/geeklog/data.

In that text file, just add whatever you want to be contained in a message to a new user. To refer to the username and password, as well as your site's name and URL, you can use the following variables (i.e. these words in curly braces will be replaced with the proper information when the email is sent out):

So your 'welcome_email.txt' file could contain a message like this:

Hello {username},

thank you so much for signing up with Geeklog France! 
We hope the site will be useful to you. Below is 
your username and password that you can use to
log into the site:

{auth_info}

We recommend that you change your password 
once you've successfully logged into the site.
Please use the following URL to change your password:

{site_url}/usersettings.php?mode=edit

Thanks again, {username}, for registering an account
 at Geeklog France and we hope to hear from you soon.

regards,
The webmaster,
{site_url}

… or something like that. The 'welcome_email.txt' makes it easy to change the text of that email, so you may want to change it more often, e.g. by adding a link to current site highlights, special offers, or things like that.