Originally Posted by
IAN-UK
Grammar doesn't come into it. But convention, comity, courtesy and just plain good manners do.
The third form is the correct way to address a stranger, though the second one is increasingly used to get round gender uncertainty.
Assuming emails come as a result of having a BAEC account or BA flight, surely they already know one's title (Mr, Mrs, Dr, Your Excellency etc) from the information one gave them, irrespective of what gender one identifies as.