IP Blocked On Our Mail Server
Like most email service providers, we are frequently attacked by hackers trying to access an account on our mail server. Usually this is so they can use your account to send out spam. A typical method is to attempt a Brute-force attack, which is trying numerous possible passwords in succession.
In order to protect our mail server from these attacks, we are using special software (fail2ban) that detects multiple failed password attempts , and then blocks the IP address where the login attempt was made for 10 minutes.
One unfortunate side effect of this is that if you have the wrong password setup in your email software, it will keep trying to log into the mail server with the incorrect password, and trigger fail2ban. This means that any other device coming from the same network (other computers or devices in your house, for example) will be blocked until the device with the incorrect password is either shut off, or updated with the correct password.