Mr McMillan is now keen to hear from any constituent who has experienced problems with Royal Mail deliveries ahead of a visit to the local delivery office later this week.
He said: “In recent weeks, I’ve been contacted by numerous constituents from across Inverclyde regarding the late delivery of mail.
“We all know how busy this time of year is for postal workers, but for one constituent this week to tell me they received only one letter which was dated the middle of November, is deeply concerning.
“I’m particularly worried about people not receiving medical appointments and/or other important official documentation in a timely manner.”
Mr McMillan said his staff have been raising each of these instances with the Royal Mail, and he will be visiting the local delivery office on Friday morning.
He is encouraging any other affected residents to contact his office.
Mr McMillan said: “If anyone else has issues they would like me to raise, please call the office on 01475 720930 or email me at stuart.mcmillan.msp@parliament.scot.”