I have imported a csv address book into Evolution, which seemed to work, and I have composed a couple of emails to different people. Their email addresses seems to be entered, but when I send them, they are immediately kicked back telling me that the recipient is invalid. It provides their email and IP address, but tells me that they are invalid. I am receiving mail, so that is not a problem. I would reply to the mails I got to see what happens, but they are more or less spam. I'm pretty sure that I have the account configured correctly, but am at a loss. Any help would be appreciated.

Can you sent the mail when you enter the email address manualy?

It does not seem to work, although it doesn't give me an error message, but there is nothing in the sent folder. Besides, when I enter it manually, it just autocompletes. The difference is that sending it by typing the name in gives the address plus a IP address, which results in an error message. This time I left the IP address off, which did not result in an error message, but it did not seem to be sent. Right before the error message I see a box that has some information on about my mailserver (not an error), but it's up for just a fraction of a second and I can't see it all.

any pointers in the logfiles?
Do you sent directly using the SMTP from your provider, or using sendmail, exim....
Is the outbox empty?
try to delete all the mails in the outbox, before sending a new mail.
You can turn auto completion off

I have not found the logfiles. I send using smtp. The outbox is empty. I will try to delete the mails in the outbox the next time I log back into Ubuntu. Thanks.