[Zope] sendmail problem

I am trying to use the dtml-sendmail tag but it is failing to cooperate. I have tried various combinations of writing the sender and mail content but i either get an error message Error type: TypeError Error value: len() of unsized object which traces back to the python smtp and rfc822 modules when i write the recipient as "To: scheirich@nulleins.at". On the other hand i recieve an empty email-message when i use the mailto="scheirich@nulleins.at" parameter which arrives correctly but has undisclosed-recipients and no content. I have tried the email address in various forms <> delimited, no delimiters, ... I am using 2.3b1 with hot fix, but i had the same problem with 2.3 Any hints anybody ? Harald Scheirich