So the addresses are now valid SMTP email addresses (otherwise you'd still see the AddressException) but your SMTP server is sending back a 550 message. That means the requested action cannot be taken, because the mailbox is unavailable to whichever user tried to preform the action, either because it doesn't exist or access is denied (you can find this out by reading the right RFC by the way).
InternetAdress validates the String is a valid Internet Address and not a valid Email address (not even in form) A lot of Strings are valid Internet Addresses but, not a validly formed email address. The failure he is getting now is caused by one of the Strings in the list. It appears to be a comma or empty String. Scrubbing a List of String to ensure each is a valid appearing email address takes a bit more work.
The problem is fixed. The problem was in the method that gets the e-mail addresses, it returned a null, cause the way how I converted my Vector to an Array was wrong.
This has fixed the problem: String[] mijnEmails = (String[]) emails.toArray(new String[emails.size()]);
InternetAdress validates the String is a valid Internet Address and not a valid Email address (not even in form) A lot of Strings are valid Internet Addresses but, not a validly formed email address. The failure he is getting now is caused by one of the Strings in the list. It appears to be a comma or empty String. Scrubbing a List of String to ensure each is a valid appearing email address takes a bit more work
Well actually the InternetAddresses class parses the String to ensure its RFC822 compliant, unless you tell it not to. 822 compliant == a valid SMTP email address. Passing a null to the constructor is not valid, unless you do as Azz Romaysa has done and concatenate a blank string onto it.