I use Yahoo Mail from Android devices. In my Sent box over the last few weeks I see a handful of completely blank e-mails (no subject and no contents) being sent to very strange addresses such as:
Other addresses include
All of these addresses (i.e., the
... in the above) start with the string
return- and are followed by a very large random-looking string/number.
I haven't knowingly shared my login information with anyone.
What could it be?