Speaker David Carter has given MPs an assurance their emails aren't being monitored, scanned or saved by Parliamentary Service.
Labour's Chris Hipkins on Tuesday complained that an email he sent to a journalist had been blocked by Parliament's communications system, which is run by the service, because it carried an attachment which had previously been a classified document.
The document was issued to Mr Hipkins under the Official Information Act.
Mr Carter said on Wednesday the classification should have been removed before it was sent to Mr Hipkins.
Because it still carried an encryption the security system that Parliamentary Service uses, called SEEMail, intercepted it.
"I have been given an absolute assurance that the Parliamentary Service system does not scan members' emails other than for spam filtering, viruses or SEEMail classifications," Mr Carter said.
Opposition MPs weren't satisfied with the situation and wanted to know how interceptions could be avoided in future.
Mr Carter said he would have a further discussion with Parliamentary Service, and with any MP who wanted to talk to him about it.