Thanks for the replies so far.
I'm impressed at your consideration for your recipients!
Usually I don't - I send the highest resolution images that I can (from my laptop over a landline) - what's the point of sending low-resolution pictures when I'm taking them on a proper digital camera?
However, I've recently become aware that sometimes I get a reply to an email that is sent from a mobile 'phone, so, remembering painfully slow dial-up internet connections, I cringe when I think that maybe the recipient of the email might struggle to view my images (or maybe even not be able to 'see' them). Worse still, if the recipient had to pay £££s for airtime just to be able to see something that would be FOC on a computer using broadband . . .
Of course, not having a smartphone, I don't know anything about what I was asking.
I don't even have a contract for my mobile (apart from PAYG) though I pay for every call that I make.