sending a mail message with the default encoding fails

[davidnich]

MailMessage::Message msg("qoretechnologies.demo@gmail.com", "Passenger account activation");
string text ="Complete activation by visiting the following link: https://lorem.ipsum.com/activate/" + activationCode;
msg.addBody(text);
msg.addTO(ah.email);

results in:

MIME-TRANSFER-ENCODING-ERROR: "Content-Transfer-Encoding: \"default\" is unknown"

note that setBody() works; calling addBody() does not result in the default encoding being set properly for sending