The following parameters can be appended to the end of an Apex button or to the end of an S-Doc creation call:

Button Values Function
&prepemail= 1 to enable, 0 to disable (disabled by default). This will create but not automatically send an email.
&did= Comma delimited list of IDs for documents from your “Documents” tab. For attaching documents to your email.
&aid= Comma delimited list of IDs for attachments on a record’s “Attachments” related list. For attaching attachments to your email.
&autoopen= 1 to enable, 0 to disable (disabled by default). This will make the document automatically open after being generated. Note that this shouldn’t be used on calls to create S-Docs, since users aren’t explicitly creating these documents in the way that they do with an Apex button.
&sendemail= 1 to enable, 0 to disable (disabled by default). This will create and automatically send an email.