Sandy Duncan, who represents Turriff and District, contacted Aberdeenshire colleagues who were due to consider a planning application for a wind turbine from a firm he was partner in.
He was found to have breached the code of conduct for councillors.
The Standards Commission for Scotland found he had acted inappropriately by using council facilities having been expressly warned not to do so.
The hearing panel found that members of the public would reasonably conclude that, in signing off his emails as a councillor, he was using his position to seek preferential treatment.
Mr Duncan was suspended for six months from a number of committees.
Panel chairwoman Julie Ward added: "Whilst accepting that Councillor Duncan had a previously unblemished record, had referred himself for investigation and accepted he should have dealt with matters differently, he nevertheless should have ensured he kept his role as an applicant and that of a councillor separate."
"A failure to keep personal interests separate and distinct can result in council decisions being legally challenged and can erode public confidence and trust in local government and the democratic process itself."
A councillor has been suspended from certain duties for six months.