A similar problem is happening on 7.0 when a Sales Order is confirmed:

Traceback (most recent call last): File "/opt/openerp7/addons/mail/mail_mail.py", line 269, in send subtype_alternative = 'plain') File "/opt/openerp7/server/openerp/addons/base/ir/ir_mail_server.py", line 329, in build_email msg['To'] = encode_rfc2822_address_header(COMMASPACE.join(email_to)) TypeError: sequence item 0: expected string, bool found

Is this related or should I open a new bug?