I can't send email, because Class 'Net_SMTP' not found. I run find vendor -type f -name "*.php" | xargs grep "class Net_SMTP", but nothing. I also composer update --no-dev.
Then I checked release tarball, I found Net_SMTP class in vendor/pear/net_smtp/Net/SMTP.php. But I can't find this file in my git installation, looks like composer.json missing pear/net_smtp.