On the Purchase Order creation page, there are options to Create and Email PO, which finalizes the PO while simultaneously sending it to the vendor.
When viewing a PO, you can email the Purchase Order by clicking Email Purchase Order in the upper right.
Email Purchase Order Window
The Recipients field is automatically populated with the vendor's email address. Additional email addresses can be added.
The Subject field determines the subject line of the email.
PDF Label Sets are created within the Purchase Order Customization settings and are used to alter labels on the PO.
The Message field can be used to include additional instructions in the body of the email.
The PO PDF will be attached to the email. Additional attachments can added by uploading files. There is no limit on the file type or number of files, however, the file size limit is 25MB.