Some of the + modules allows to send mail with customized message. In that case a Message field will appear and you click on the field to open the message editor.
Here you can compose the message to use as the mail body when the mail is sent; the mail body may include fields from the object (the quotation or invoice etc.) or the associated company etc. To insert a field in the message you click on the field in the right side list of fields; the field will be inserted where the cursor/caret was located; the field will appear as something like %quotation:title% or %invoice:duedate% etc.
Once you have composed the message you click on the Save as template button and give it a name; you will then be able to select the template in the template list in the top right corner of the message editor.
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