Easiest way I find to test this is to...

1)

a) install fakemail and run it
b) tools->options->writer->mail merge email
c) localhost 8025

2)

a) type some text into writer that will exercise utf-8, e.g. "Caolán's test"
b) tools->mail merge wizard->next->email message->select address book
c) create, add one user with your own email address, ok
d) next, next, text, send merged document as email
e) and test all of plain text, html and the various attachment options

fake mail will dump the mail it gets into its pwd, if all that works, you can
then try with your own normal mail server.