Read on about what it is, why it is useful, and how to find your mail index
When we sign-in to multiple Google accounts on a device's web-browser, each mail is assigned an index number, or a position number, so to speak.
The account with which you first logged in gets the index 0. The next account gets the index 1 and so on. These indexes look like
u/1/ in links. Here, index 1 is chosen as an example. Sometimes it also appears in the form of ?authuser=1.
They all really refer to the same idea. Positioning or indexing the accounts.
The Index 0 Mail is your Default Mail. Appears as u/0/.
Different services are available on different Google accounts. And then, if some of those accounts are a GSuite account and belong to an organisation, there can be many levels of restrictions.
Whenever you open a link, the Google Account Picker goes through your indexes in order, and usually opens up with the correct account. However, sometimes this is not enough and you need to manually choose the account with which to open the link. This is where index number comes in handy.
If the links mention an index number in it, and if it matches your correct organisation account, you can easily access the resource without having to go through the step to pick the correct account.
This site helps you pick your correct account index and modify all dependent links accordingly, so you can have a more friendly experience.
It's actually pretty simple. Just go to mail.google.com and change accounts to your IISER Pune Student Email ID. If you cannot find your student email ID, you need to Log In first.
Now, notice the URL. It will look something like this: https://mail.google.com/mail/u/2/#inbox. Do you see
something similar to the u/2 part? The number after u/ represents your account index. That's it.
Now, every time you visit the page, if you know your account index, just choose it directly. Else, if you are on a new device or if you forgot, just follow the instruction above once more, and you will know the account index.