Why am I receiving emails from unknown senders?

Identify if the email is spam

If the sender is unknown and the subject line is odd, it is possible the email is spam and should be deleted.
Check your settings for blocked emails

Look at your email setting, as the unknown sender may have been inadvertently blocked.
Check for email filtering rules

Sometimes emails are filtered according to certain rules you may have set and are moved to a different folder. Check to see if this is the case.
Contact the sender

If the email is not spam, contact the sender and inform them that you are having difficulty receiving emails from them.