Is a yahoo.de email address the same as a yahoo.com address?

Hello, I have the following question/problem:

I have an account on a website for which I have an email address with yahoo.com. However, my mail app only shows the yahoo.de address. For example, if I want to send a verification code to the yahoo.com address, it doesn't arrive at the .de address, which leads me to conclude that these two addresses are different. However, if I try to log in to my mail app with the yahoo.com address, I'm automatically logged in with my yahoo.de address, where the verification codes don't arrive for the yahoo.com address. Another piece of information: everything before yahoo.de and yahoo.com is the same, so myname@yahoo.de and myname@yahoo.com

Can anyone help me?

Many thanks in advance!