Kindly refer following article , this should help:

https://pdn.pega.com/forums/java-activities/send-email-attachment-without-work-object

I am using 7.1.6,

I tried the following scenario from the pdn forum, which is posted below, but i am not understanding the "datatoattach" value what should be sent, i am assuming the pyAttachStream content should be decoded to base64. please correct me if i am wrong.

1)Create a new page called Attachment Page of class Data-EmailAttachments
2)Use the java method to write the following piece of code.Pls note that the variable below datatoattach should contain a Base 64 Encoding of the entire attchment.Use Base64Encode expression to do that in some prev step.

------------Start of code-----------------------------
ClipboardPage page_EmbedAttachment = null,
page_AttachmentPage = tools.findPage("AttachmentPage");

ClipboardProperty prop_pyAttachment = null;

try {

prop_pyAttachment = page_AttachmentPage.getProperty(".pyAttachments(<append>)");
page_EmbedAttachment = prop_pyAttachment.getPageValue();

page_EmbedAttachment.putString(".pyData",datatoattach);
page_EmbedAttachment.putString(".pyName","XYZ.xls");
page_EmbedAttachment.putString(".pyDecode","true");
page_EmbedAttachment.putString(".pyRemoveXML","false");

} catch (Exception e) {

tools.getPrimaryPage().addMessage( e.getMessage() );

}