have you tried deleting the mailer-daemon email
i found an easy way to deal with this.
it is not a malformed message. it's the standard mailer-deamon message. but for some reason email clients (and even the online- inbox) try to display the attachments of the message that didnt make it to the other end. and i guess, the system is having a hard time interpreting a 7,8MB mp3 file in ascii letters and therefor it is not possible to delete the mail...
anyway, in the directory >home/user/.evolution/pop/< i deleted the dir that holds the account information. (in my case >firstname.lastname@example.org@pop.gmx.net<. so evolution doesnt know which emails have been downloaded in the past and is forced to download them all.
the good thing about this solution is, the other accounts, settings, "sent" folders and so forth stay unharmed!
first, of course, it is imperative to delete the mail, that is responsible for that mess, online so it will not be downloaded again.
thx for your help.