AmazonFire tablet HD10

There is no Fire tablet that will operate on cellular and you have published this question in a cellular forum.  

Any Fire tablet you own would be Wi-Fi only which means internet.

It sounds like it's an email problem.  

There is a separate forum for email issues

Technically, there were a few 2nd, 3rd and 4th Gen Fire tablet models between 2012 and 2014 that offered LTE capability.  But those are long out of support today.  The 7th Gen models are barely supported today as they are up to the 12th Gen models now.

@roselee_Gabby , I'm going to assume you are already on wi-fi because you really can't use that tablet to any real degree without a network connection of some kind to begin with.  You can with limited capability, but depending on what you do on it, it will quickly begin to complain about not having a network connection.

Do you know which generation your HD10 is?

How are you trying to access your email? 

Are you trying to set it up in the Email app on the tablet itself?

Can you access another way - like on a PC?

One possible issue could be how the email server works.  I'm not positive about who manages AT&T's email these days, but I think it's still Yahoo.  And Yahoo has a history of their email services getting hacked.  Now, they implemented more modern security requirements such that you need a more modern email client app that works with the newer security protocols. 

I think the email app that Amazon includes as the stock app on their tablets is based on the basic open-source Android email app. Depending on the generation of your tablet, yours could still be based on Android 9 which is now 4 and a half years old.  The operating system on the Fire Tablets are based on the open-source version of Android, and Amazon heavily tweaks it for their own services, and they tend to be several Android versions behind the rest of the world, but they don't have their own email app.  So the stock Android 9 email, calendar and contact apps are there instead.

There are ways around it - usually meaning you have to go the email service on-line, through your PC browser, find the settings, look for something about allowing less secure email clients, and it may involve setting up an app specific password - which is not your regular email password.

But, it's easier to just use a more up-to-date modern email client app.

You could try the Microsoft Outlook app from the Amazon App Store.  I have it on my HD 8 and it does work.  It is also regularly updated and will support the email services with newer security protocols.