If you find that HOudini has stopped retrieving you email it is probably for good reason.
Cause
Houdini may quarantine a email account if it finds that the email account keeps receiving email with headers missing any tracking information or the email contains a virus. You can confirm by looking at the logs located in the in the logs folder. The log containing any errors is called catalina.out or error.out depending on the OS Houdini is running on. Open the log with text editor on Windows or Console on OSX. If you see warning from Houdini about email missing a MSG ID or a Virus has been detected then this is the cause. Houdini has quarantined your email account to protect the host machine.
Solution
You can bump the HoudiniESQ service (restart the service) by running the stop Houdini Service in the HoudiniESQ menu (Windows only) or you can stop and start the service in Windows via the Control panel. The Houdini service can have a number of names depending on the OS e.g. houdini, catalina, apache or tomcat. When you bump the server houdini will ignore the quarantine until it sees another infraction. To avoid this possibility it is best to identify who is sending you those emails and set a filter on your email server to ignore them. Currently Houdini has no mechanism to apply Email rules on the server side so you will have to do it from your Email service providers end.