User in windows server 08 active directory keeps getting locked out

A user keeps getting locked out every morning. He is typing in the correct password, and confirmed this. He's using only a laptop and cell phone to log into his email. The email system is outlook 2013. There was only one other user who had a similar problem, it came from having multiple devices on and online requesting the password. I checked to see if any mapped drives needed updated info, but the drives were all up to date. I've been told to use eventcombmt on the AD, but I'm not familiar with it. Any suggestions/tips/ideas. Thanks! -MG