Sounds funny? Reading the header of the post again? Yes it is still how to select all your mails in Gmail. You can set your inbox to show 25 emails at once. So when you click the checkbox for select all it will only select all the 25 mails. So how to select all your mails in your inbox? You might use this to delete all the emails in your inbox or select all mails in your inbox to mark it as read.
This is very simple as you think, click the select all checkbox, when you do this you can see a link next to the text ‘ All 25 conversation on the page are selected’ saying ‘Select all conversations in inbox’ as shown in the screenshot below.
When you click that link all the mails in your inbox gets selected.