We've installed 3.0.10 a couple of days ago and found that our emails are not being sent. After some investigation I found something that looks like a bug.
File includes/functions_messenger.php, line 720:

if (!file_exists($this->cache_file) || filemtime($this->cache_file) > time() - $config['queue_interval'])

I believe it should be

if (!file_exists($this->cache_file))

as

|| filemtime($this->cache_file) > time() - $config['queue_interval']) 

is a leftover from a stale lock check from old locking system, which used to be

if (!file_exists($this->cache_file) || (file_exists($this->cache_file . '.lock') && filemtime($this->cache_file) > time() - $config['queue_interval']))

and which used to work correctly due to && operator having higher precedence over || operator.