Thunderbird is a desktop mail client.

Ask about Thunderbird portable here. Portableapps.com

dtThunder said

This question is important. I need to access my email from my mobile and from any computer. Thanks.

Portable Thunderbird from https://portableapps.com/apps/internet/thunderbird_portable is the same as Thunderbird for Windows from https://www.thunderbird.net/

Only difference is it is more self contained with its own launcher so it can even run completely off a usb flash drive on Windows OS's, hence the "portable" in name.

There is no mobile version of Thunderbird for iOS or Android.

dtThunder said

This question is important. I need to access my email from my mobile and from any computer. Thanks.

Then you need to be more concerned with email server protocols than which email client software you use.

Read up on how IMAP email protocols works and how it differs from using POP.