how do I change my internet address for launchpad?

Today, I changed ISP. I have changed all the necessary fields in Edit, Preferences, Mail Account and can receive mail but am unable to send it.

I have downloaded Thunderbird and have sent messages via that programme without any problems. I did note, however, that my old email address as well as the details of the old ISP came up by default (in Thunderbird). After changing those, everything worked perfectly.

Not so in Evolution, where my former ISP still retains some control. I think that there must be a control file somewhere that stores those parameters. But where is it?