It looks like there have been a few fixes since 8.x-2.0:
🐛
$emailAddress must be a valid email address
Fixed
is a pretty important one if it affects a site as it causes data to be lost.
🐛
Warning/error generated when sending to CC or BCC without name
Fixed
seems like a nuisance, but ideal for that not to happen.
It seems like a great time to make an 8.x-2.1 release to get those fixes onto more sites.
Fixed
2.0
Code
2 things that could be worth fixing, after looking at the queue for bugs:
🐛
Stats data variable name mismatch
Fixed
the statsdata variable is misnamed.
🐛
Improperly implemented interface \Drupal\Core\Mail\MailInterface
Fixed
the function signature is wrong
Automatically closed - issue fixed for 2 weeks with no activity.