Author's email address in a published paper is not working I have stumbled upon a paper that is very related to my field of research and after reading and discussing it with my supervisor, I found some issues in the paper that I need more information about, such as the data set they used.

When I sent them an email (their emails are university email accounts) I received a failure notice telling me that these emails have been discontinued.

What is the protocol that I should follow to pass my inquires to them?

I have found one of the author's LinkedIn account, from it I know his current working place, can I contact the company asking them for his contact information? And I have already sent him a connection request containing a brief message of my intentions.
There's no particular "protocol"; just try to find some other way to contact them.

I would try:


Google the author's names.
Look for more recent publications by the same author(s); see if they list updated email addresses.
LinkedIn was a good idea.
If you have found the author's employer, see if you can find his contact info on their website; or contact someone else at the company and ask.
Some professional societies maintain a database with contact information for all members.  For instance, mathematics has the Combined Membership List.
Contact someone at the previous employer and ask if they have current contact info.