Odoo verion: 10

OS: CentOS 7

When using "Send RFQ by Email" or "Send PO by Email", we are consistently seeing cases where the email is sent only to the vendor. Followers of the document and people added in addition to the vendor do not receive an email. In checking maillog, we are only seeing an attempt to send an email to the vendor. No attempt appears to be made for other recipients. I cannot see anything helpful in the Odoo logs, only a mention of sending the email.

Has anyone else encountered this issue or know of additional debugging steps that we could take?