Version:           1.9.1 (using KDE KDE 3.5.1)
Installed from:    Fedora RPMs
OS:                Linux

When sending a mail to a large number of people, it is common to use the RFC2822 'group' construct, and to put the actual recipients in Bcc:. The 'To:' header will look like this:

   To: People invited to my party : ;

kmail doesn't seem to let me send that -- it complains that the address contains an invalid character.

If the group is empty, kmail also attempts to qualify it -- it turns it into 'People invited to my party : ;@infradead.org' before complaining of an invalid character. If the group has an address in it, kmail merely complains that 'People invited to my party : ;' has an invalid character, and the address is not shown in the error dialog box.