Not in spam.
However I checked in sent (again) and found my reply - with the lost message.
So no sign of the original message in inbox but comes up in the sent messages box (ie reply to this message)
All solved now but was to do with someone moaning they hadn't been paid - when they had.
Strange as it was reasonably important and was lost (for a while - though I did have a printed copy)
One of those glitches that show you have to keep an eye on everything.
Sorry - rather boring.