There isn't one.
There are most likely either 1 or 3 possible issues
1) Sudoers is messed up. Take a look at the wiki for how to fix that
2) You arn't using Bash: sudo /bin/bash
3) You arn't su-ing from root, or you arn't using sudo
a) If you're root, then su - zimbra
b) If you're not root, then sudo su - zimbra |