Suddenly and for no apparent reason I could not send emails from my iPhone when connected to Vodafone's 3G network.
Error message - " cannot send mail. The connection to the outgoing server "mail.btinternet.com failed "
Receiving emails was not a problem.
I complained to my broadband supplier (BT) who referred me to Vodafone as they insisted all my settings at BT's end were fine.
Vodafone said that the settings on my SIM card are updated from time to time to keep the correct settings on the phone so that it can communicate with BT's servers correctly. However my phone only updates when I'm connected to the 3G network (won't update when I'm on wifi) and I might have missed one. I was advised to send an SMS message (ie with the word "web") to the number 40127 the reply to which contained a link that allowed me to download an up to date.
2 hours later my phone was back to working as it should.