Maybe you should try other email client software. It is android so you have a choice of other email software if the stock one screws up.
I have a Samsung Galaxy S3 Mini, which I have had for exactly one year. I had two email accounts on it; My personal email and my university one. They were both working fine until about one week ago. When my personal email account went to sync, a notification came back that it couldn't as the password was incorrect, so I retyped the password but the same notification came back 'password incorrect'. I then changed my password and entered the new password into my phone; same notification appeared! This kept happening for two days so I removed my personal email account from my phone and went to re-register the email account. The first time I entered my details it said 'incorrect username or password' so I re-entered it and it said 'unable to connect to server'. I have tried numerous time's but every time I do it comes back either of the above responses. I have also chosen all three account types (POP3, IMAP and Microsoft Exchange ActiveSync) and none have worked.
The other email is working perfectly fine and the email (personal) is working fine on my computer.
Can someone help me?