How to send Email with attachment in Siebel Workflow

• Design the workflow.
• Add new Business Process step on workflow canvas.
• Add below Business Service Name and Method.
• Business Service Name: Outbound Communications Manager
• Business Service Method: SendMessage
  

• Now go to "Multi Value Property Window" and Input Arguments and set the arguments as below.
• AttachFileList > Attachment File path (C:\Siebel\xx.0.0.0.0\ses\siebsrvr\temp\S-WEB-APP_8364_9620_0_Attachment Name.pdf)
• CommProfile > Communication Profile Name through which Siebel will send the Email
• MsgBody > Email Body
• MsgSubject > Email Subject
• MsgToList > Destination Email (t@t.com; a@a.com)

• Save the workflow deploy and test.

If you need to add attachment from Siebel Contact, Service Request or Case attachment please check the below article:
How to get Siebel attachment as file in Workflow

If you don't know how to configure or find the working "CommProfile" parameter value please check the below article:
Setting up Communication Profile for Sending Email from Siebel