Dave Justus says in re an article at Forbes:

Yahoo! is standing by its policy of protecting the privacy of its e-mail subscribers, spokeswoman Karen Mahon said. This is an interesting dilemma. Should an email account and the electronic documents it contains be considered part of an estate, to be transferred to the heirs of a person after death or should it remain private? Typically I believe traditional letters would become the property of the heirs but one could argue, as I guess Yahoo! is doing, that email accounts do not automatically transfer.

I think that in this increasingly digital age, this is going to become more of a problem. I know that if I were to die today, there are three sites that would die as well, as my brain is the only place the passwords are kept.

Passwords and accounts need to be willed. One should leave specific instructions on how to handle all of ones affairs - and now days that includes Blogs, Websites, email accounts, Pay Pal accounts, Ebay - the list goes on and on.

I side with Yahoo! on this one - unless there are specific instructions in the Will of the person that gives his or her heirs the rights to access the accounts. There could be information in the email that perhaps he did not want people to read. We do not know. With out more specific instructions from the deceased, I feel that we should not impinge upon his privacy.

— Tsyko

Update 11/2017: You are using a password vault now right? Lastpass and 1Password are a really good choice. I personally prefer 1Password but choose the one that works for you.