Hi Lauraine,
WikiTree will have the correct email address for all members ... that is, the correct address at the time they signed up. If a member changed their email address after that, then WikiTree will not know about it unless the member entered the new address in his/her own profile.
There is no need to waste your time trying different variations - email addresses are not case sensitive, so it doesn't matter if you use upper or lower case for any letters in the address. If you received a private message and clicked the "reply" button in your email program then the email address the person entered at the time they sent you the private message will automatically be in the "to" field of your reply message.
Here's the kicker - when you send a private message, you have to fill in the email address field or it cannot be sent. If you don't want to reveal your email address to the person who will be receiving the message, then you can change your email address that shows in the private message to something else. It sounds to me like that's what the person probably did ... and the result is that your reply goes to an invalid email address. There is absolutely nothing you can do about it and there is nothing WikiTree can do about it either.
If the person is a WikiTree member, then you can contact him/her by sending him/her a private message, otherwise I'm sorry to have to tell you this, but you are out of luck.
