Thanks, Speccers. It's just puzzling that all works fine from UK Explorer wi-fi W-LAN hotspots, but I'm currently unable to send from Vodafone D2 hotspots unless I use mail2web or a similar web-based mail service.
I keep asking Vodafone what the outgoing mail server should be set to - I can easily create a bespoke W-LAN e-mail account but just need to know the server name!