I have a user using outlook 2013. I'm on exchange 2013 as well.
The user has her main account which works fine, but she also has a 2nd account, that periodically throughout the day, a login prompt keeps prompting her. Even though she enters the correct password, it still prompts.
When i sent to the settings and tried a test send, I do get an error message. It's strange as it's an account on my exchange server just like every other account, I don't understand why it's asking for the password, when she enters the password correctly.
How do I fix this? Thanks