E-mails with attachments were hanging during the send process and then
timing out. I am now fairly sure that increasing the server timeout
setting from a default of 1 minute was the answer. I just wish that
I'd realised this simple fact sooner but, having only recently switched
to broadband, I had never encountered this issue before.

For information purposes, this setting is found in
Tools\Accounts\Properties (button)\Advanced (tab). If a user has more
than one e-mail account, it has to be altered for each account.

Thanks for all the input everyone. It's really due to you that I
re-evaluated my approach and discovered that I had overlooked something
quite elementary.

TC