I use Drupal 8.7.3 with Commerce 2.
When the order process is complete, the confirmation email is sent, but the HTML tags are deleted.
The email has "content-type text / html; charset = UTF-8;".
Key value 8-bit content transfer coding content type text / html; character set = UTF-8; date Tue, 18 Jun 2019 23:39:22 +0000 of "Linux user"
mime-version 1.0 received by localhost (sSMTP sendmail emulation); Tue, 18 Jun 2019 23:39:22 +0000 sender email@example.com confirmed order # 2 at firstname.lastname@example.org x-mailer Drupal