g4msmail_addAttachment is used to add an attachment to an email with the G4MSMAIL functions.
The maximum size of attachments is 16meg. Files larger than this will be ignored.
There is a maximum number of 100 attachments allowed.
Returns: total number of attachments for success, -1 for error.
File - Specify the fully qualified path to the file which should be located in the IFS to attach.
File Name - The name of the file as it will appear in the email
Error Message (output) - Error message
no_attachment_action - Specify *ERR for this value to have this function return -1 if an attachment is not found.