Yes, you can have an event trigger an email. If you want the "trigger" to
be the act of completing a textbox control on a form, use the control's
After Update event.
There are a number of techniques available to open your MAPI-compliant email
client from within Access. The simplest of these is the SendObject method,
which you can review in VBA Help. You might also want to investigate using
Automation with Outlook. There is sample code at the following links that
can get you started:
MSDN article on creating appointments, emails, etc., using Automation
http://tinyurl.com/2knwj
Q161088 Using Automation to Send a Microsoft Outlook Message
http://support.microsoft.com/?id=161088
HOW TO: Use Automation to Send a Microsoft Outlook Message using Access 2000
http://support.microsoft.com/?id=209948
ACC97: How to Use a Recordset to Send Outlook E-Mail to Multiple Recipients
http://support.microsoft.com/?id=318881
Also, have a look at Tony Toews' email page:
http://www.granite.ab.ca/access/email.htm