Email fails to send and gives the error 'SMTP Server not specified. Check Tools, User Preferences, Messaging, Email.'

Sending an Email may give the error 'SMTP Server not specified. Check Tools, User Preferences, Messaging, Email.'.

This occurs if an SMTP Server is set up under Global Settings, Messaging, Email and, under User Preferences, Messaging, Email, the box is checked to 'Use details defined under Global Settings.'.

To work around this issue, uncheck the 'Use details defined under Global Settings.', enter anything, e.g. 'X' as the SMTP Server and then recheck the 'Use details defined under Global Settings.' box.