after 2 hours of debugging the JavaMailContainer and working with javamail properties and network traces i noticed that when creating the JavaMail session the Container transforms all property names and ALL property values (including the password) to lowercase. Thus authentication fails if the password does contain uppercase characters.
The attached patch removes the conversion of property values to lowercase altogether, which fixes the issue. As i see no pressing issue to convert other property-values to lowercase i chose this way instead of excluding only selected properties.
The second change to the Container prints out the Text of the exception which has occured when reporting that the mail store could not be opened to give the user a clue about the source (i.e. SSL trust chain verification problem).