First of all, you have to understand that you will not be able to UNLINK the additional e-mail address!
Before linking an additional address, you will have to bind your account to a cell phone number.
How to link?
Proceed to your Gaijin.net store Account protection menu:
In the E-mail address section press Settings:
Please note that the additional e-mail address should not be previously used for any other account in our database.
Enter your desired e-mail address and press Add.
You will receive an SMS with a code via phone number previously bound to your account. Enter this code in a text field and press Confirm button
After this an automatic confirmation request will be sent to your additional address
Follow the link from that email in order to confirm your address
For security reasons you will be able to use the additional account as your login not earlier than in a month after the binding.
Now you will be able to take a look at your log in history in the E-mail address section
How to block logins from the additional e-mail address?
After the binding you will receive a notification to your main e-mail address thus letting you know that additional address was linked. If needed, you will be able to block the operation.
In order to confirm the block, you will have to enter the code you will receive via SMS
Wen it's done, the additional e-mail address status will change to "blocked"