Do you have another e-mail client/program installed? If not, then why not let Thunderbird be your default e-mail client/program? "System Integration" means that it will tell Windows that any attempts elsewhere in Windows to send an e-mail, should trigger Thunderbird.

If you do want another program to be the default e-mail program, then try this.

First, make sure that the other e-mail program is set to be the default e-mail program in Windows:

Open the Windows Action Center (click the icon in the bottom right corner of your screen, which is to the right of the digital clock). Click on "System", then "Default apps" on the right side. Under "Choose default apps" on the right side, click the e-mail program, and change it to your preferred e-mail program.

Now in Thunderbird: Thunderbird menu: Options: Advanced: General tab: Click "Check now"

Uncheck Email and Newsgroups (or whatever you can and want to uncheck), then click on "Set as Default", which means only "OK" or "Apply" in this environment. (See image).

Then it should not appear again.

This solution was originally in this question .

Wow, Bruce... You have provided one of the best responses I have ever seen in a forum!!! It is very well written and easy to follow... This worked like a charm!!! While I do not have a Windows Action Center icon in my notification area, your guide was so well written, I was able to achieve the desired effect anyway... Thank you very much for your help!!! Bill

I recently installed Thunderbird after my hard drive crashed and burned. I now receive the same message popping up at every start-up. Thunderbird is set as my default email program. I've checked skip integration and set as default. I've looked through every program I can think of to find a conflict without success. When I tried the suggestion above, I did not find system when opening the fly-out near my clock. When accessing system through my control panel, I do not see the option for default apps. I've already looked through default programs in the control panel. I looked through internet options and set Thunderbird as my default. What am I missing?

Also, since the new install, my emails are being auto-marked as read as soon as they download. I've unchecked the box for the auto-read option. Computer has been restarted. No success. Outlook is installed on this computer, but I do not use it. I did not set up email addresses for that program. Any thoughts?

Thanks for any help with both problems!

MsBeeTree said

I recently installed Thunderbird after my hard drive crashed and burned. I now receive the same message popping up at every start-up.

Please read all the Forum rules and guidelines. Of importance here is:

Posting support requests
Create one thread and only one thread for each subject you need help with.
Do not re-use existing threads started by others, even if they are seemingly on the same subject. Ask a new question instead.

But please do read all the Forum rules and guidelines before continuing.

There are good reasons for this:

Do no re-use existing threads started by others: 1. The thread you posted to is closed. Normally no one will be notified that you posted in it. I was only notified because I contributed to the thread and had not yet removed the thread from my notification list. 2. Your situation is not the same as the original poster's. 3. When you start a new thread (Ask a question), some of your computer information is available to people, like your computer operating system and its version. This is useful to us.

One question per thread: This makes it easier for searches in the future. A good solution to a second problem can hide from searches when the subject of the thread doesn't mention the second problem.

Please Ask your questions separately. I will answer them personally (if you want me, and not someone else), if you then send me a personal message with links to those questions.

Apologies for my mistake. I saw the "I'm having the same issue"

and acted upon it.  Overcoming numerous computer issues with this hard drive failure.  I will figure out how to start a new thread tonight when I have more time.  Thanks!

I've tried every suggested fix, both checking and unchecking the 'Always perform...' box and using the 'Options' tab in the way that was suggested,despite the fact that Thunderbird IS my default E-mail app, but I still get the 'Integration' dialog box at every startup

https://support.mozilla.org/en-US/questions/1149318

The fix going out in the next version. It might take 1-2 weeks to ship the new version 45.6.0