Are you getting the following error from your horde imp based webmail ?
TOO MANY CONSECUTIVE PROTOCOL VIOLATIONS
This error can be caused when you create a filter that is sending invalid commands to the IMAP server that the webmail is connecting to.
A couple solutions include removing the problem filter or upgrading your imap server to a package/version that supports the commands being generated by the horde/imp webmail client.
If you are a webmail user and not the mail administrator you can uncheck your setting for "Apply filter rules when mailbox is refreshed?"