locked out

Trouble accessing email might be caused by
Wrong username / password.
Locked user in Zimbra - too many tries with wrong password (not IP based).
IP block on Zimbra - too many tries with wrong password (IP based).
IP block for the whole I-MATH infrastructure - too many tries with wrong password (IP based).
To track down the problem:
Open https://mail.math.uzh.ch - log in with your I-MATH account. For the most user, the I-MATH account is identicallly to the UZH shortname.
Success: continue
Fail: 
Does the website load correctly but shows an error 'Wrong password'? 
Sync/set your password under https://math.uzh.ch/account - Warning: if your I-MATH is different from UZH shortname, ALWAYS use the I-MATH account!
Still problems: contact Support - your account might be locked on Zimbra.
Does the website timed out? Your IP is banned, contact Support. Best together with a screenshot of your IP address https://www.whatismyip.com/
In case your email program (Thunderbird, Apple Mail, ...) has a problem:
Typically the password is saved separately for sending (SMTP) and for receiving (IMAP). Change both!
Switch off the WLAN on all of your devices but one - start with that one.
Start your email program and send a mail from your I-MATH account to your I-MATH account.
Wrong password: set the password again in your mail programm. Important: If you use Apple, reboot your device after changing the passwords! Apple Mail is known to still use the old password.
Still wrong password? Check if (1) is still fine - if yes, your account is fine (not locked), the problem has to be in the Mail configuration.
Repeat step 2 with all of your devices.