Thanks for the replies everyone. I’ve been wondering for sometime and what made me think this is an issue was something in today’s Guardian about Boomers talking to Zoomers (or something!) This is what made me think:
John Lee, 61, Dundee
Scott-Turner: I have 10,000 unopened emails.
Ayo Ogunleye: If I emailed my friend saying: “Do you want to meet up?” they’d probably laugh. Phones are here for a reason.
Baggaley: The only people who email me are Uber Eats and Sainsbury’s.
Good point Kirstea. I’m all for asking my guests what they want.
Because I’m in the hospitality business and as I want repeat business I go out of my way to give them what they want.
I think you maybe right Gareth. Follow up with a quick text after a few days saying did they get it. But I’ll start with Kirstea’s suggestion first and check how they want me to contact them.
Not sure, since in all cases they HAVE communicated with me by email and I them when they are booking – at that point they are making an effort to keep in touch. Afterwards, not so sure. 
Thanks @graham – I’ll explore further, especially if they say they do prefer text contact.