If you are switching from Thunderbird to Outlook, then do you still want help with this Thunderbird issue?

If so, then we will need details of what the error/issue is you are having. What you wrote is confusing and difficult to understand.

I say Always get this msg "System Integration" Attached Screenshot. I search Google and do everything, but not resolved.

I need to stay with Thunderbird Because Outlook use heavy data than thunderbird, when going to check mails.

and more features(secure)

Do you mean that you always get this "System Integration" window whenever you start Thunderbird?

Yes, Every time

Every time get System Integrated, msg

No way to remove it, I removed and reinstalled, Remove all mail accounts

But problem is same

OK. You never said that this was the problem. Even your screenshot did not illustrate your problem. Next time, please state what the actual problem is, instead of making people like me try to guess.

Your screenshot does help, though. It shows that you already have the settings we here would have suggested to solve this issue.

So:

1. Reboot the computer. Never underestimate the power of rebooting Windows!

2. In Windows 10 settings, make sure that Thunderbird is set to be the default e-mail program. In Cortana search, type "Default", and click on the best result, "Default Programs"

3. In that same "Choose default apps" window, scroll down to the bottom and click "Set defaults by app". In the "Set Default Programs" window that opens, find "Thunderbird" on the left side and select it. Then click "Set this program as default" on the right side.

4. Reboot computer.

If the problem continues, then in that Options window you show in your screenshot, check-mark "Always check to see if Thunderbird is the default mail client on startup". Quit Thunderbird. Start Thunderbird again, then un-check that options, quit Thunderbird and start it again.

If the problem continues after this, then I don't know right now what to do.

I set Thunderbird as Default Email client.

Then Restart PC

Then Open Thunderbird (Get same "System Integrated msg)

Close it

Then go to settings and check "Always check to see if Thunderbird is the default mail client on startup"

OK, and Restart Software

Get same msg agian

Then go to settings and Uncheck "Always check to see if Thunderbird is the default mail client on startup"

and Restart

Get error same as previous

Next in System Integrated msg box . Check "Always perform this check when starting Thunderbird"

And press Set default button

Then restart

Then Uncheck " Always perform this check when starting Thunderbird" on msg and press Set default button

Then restart

same error.

Then next time press Skip Integration button and restart software get same smg again

Problem still not resolved

Update to Thunderbird 45.6.0. See https://www.mozilla.org/en-US/thunderbird/45.6.0/releasenotes/