Cannot reply to PM sent from the forums

As I cannot find a category for this I shall post here. I have a person on the forums sending me PM which is ok but I cannot reply to them. I get this message.

Delivery incomplete

There was a temporary problem delivering your message to noreply@flightsimulator.com. Gmail will retry for 23 more hours. You’ll be notified if the delivery fails permanently.

Hello @TrevKiwi,
You will need to reply through the forum and not through the link in the email sent to you.