Customizing the E-mail Notification message

I've just installed the Advanced Guestbook and just about everything is working fine. However, there seems to be a limit to the number of characters for a customized e-mail notification message. When I enter more than, say, 6 lines of text, then the words begin to get truncated.

Basically I want my thank you note to be in both English and French, with an additional line showing the URL for my web site. I can get the English and French text in, but it cuts off the URL.

Is there a setting to adjust this, or am I stuck with this limit?

Thanks.
Gerry