re : I should mention at this point that he is using a decrepit Windows XP machine.

The last Thunderbird version that could be used on an XP was 52.9.1

re :Ever since then, now he gets "incoming server already exists" no matter which e-mail account he tries to add. Sounds like he did not delete the profile, it cannot exist if it was fully deleted.

He would have needed to : Exit Thunderbird first if it was running. This is important.

Delete the 'Thunderbird' folder as shown below; assuming everything was installed in default location. In XP his profile would have stored here:

• C:\Documents and Settings\<Windows user name>\Application Data\Thunderbird\Profiles\<Profile name>

He would need to not search, but actually locate that directory to ensure he was in the correct place.

Note: The Application Data folder is a hidden folder; to show hidden folders, open Windows Explorer and choose "Tools → Folder Options → View (tab) → Show hidden files and folders".

Then delete the program - delete 'Mozilla Thunderbird' folder located here:

• C:\Program Files\Mozilla Thunderbird\

Then empty the 'Recycle Bin'.

Restart computer.

Download version 52.9.1 http://ftp.mozilla.org/pub/thunderbird/releases/52.9.1/win32/

click on appropriate language eg: En-GB (English British) Install as standard (not custom) installation. Run to create automatic profile. Add accounts.

Note: Gmail

'Authentication Method' = OAuth was available in version 52.9.1 It became available in version 38.0.1

Add the gmail account. File > New > Existing Mail Account Enter name Enter full gmail email address Enter Password (same one used to access webmail) Select checkbox to remember password click on 'Continue' Let Thunderbird try to locate config data Make sure 'imap' is selected. Then click on 'Manual Config' button

Double check Incoming 'imap' is selected and all server settings are correct. imap.gmail.com port: 993 connection security: SSL/TLS Authentication : 'OAuth2'

outgoing: smtp.gmail.com port: 465 connection security: SSL/TLS Authentication : 'OAuth2'

'username' is the full gmail email address

click on 'Re-test' when ok click on 'Done' You will be prompted by gmail to enter email address and password in a browser that auto opens. Password is the one used to logon to see webmail account. Gmail is checking you really are you. Then gmail creates a token that is auto saved in Thunderbird in the same place as passwords.

Thank you for the steps. He says he followed them, and it still hangs at checking for password. Does this look like the right settings? : https://imgur.com/GlVMZ46

Server name already exists sounds like he is not following the steps.

Try these instructions to remove what already exists.

In the windows run dialog. (windowskey+R) Type %appdata% and press enter. Have him locate the Thunderbird folder that will be displayed in the windows file manager and select it and press the delete key.

I have seen a lot of folks get instructions to delete something and they type the file into windows search, get a not found result and then confirm they did it. So I am anything but trusting.

I did try and look at the settings, but I gave up, they never downloaded. The following link is to the correct settings for Gmail that Thunderbird looks up when trying to set up a new account. It is an XML file, but the what setting is what is fairly obvious. https://autoconfig.thunderbird.net/v1.1/gmail.com

Note this part particularly well. I have had extreme issues with anti virus product messing up account creation. Either blocking the site with the account setting I just linked to or in the case of Norton, just blocking the wizard entirely because it was a "threat" until I disabled something called sonar, so you may not be dealing with a Thunderbird issue at all. It just looks like it.

These following instructions are the next logical step to try once all the old stuff is actually deleted.

• Restart Thunderbird with add-ons disabled (Thunderbird Safe Mode). On the Help menu, click on "Restart with Add-ons Disabled". If Thunderbird works like normal, there is an Add-on or Theme interfering with normal operations. You will need to re-enable add-ons one at a time until you locate the offender.
• Restart the operating system in safe mode with Networking. This loads only the very basics needed to start your computer while enabling an Internet connection. Click on your operating system for instructions on how to start in safe mode: Windows 10, Windows 8, Windows 7, Windows Vista, Windows XP, OSX

If safe mode for the operating system fixes the issue, there's other software in your computer that's causing problems. Possibilities include but not limited to: AV scanning, virus/malware, background downloads such as program updates.

Once a new version of Thunderbird 52.9.1 program has been installed, it does not need to be deleted again.

If he gets "incoming server already exists" error message at the first attempt to create a mail account after following instructions, then it is likely he did not correctly delete the 'Thunderbird' folder that contains the 'Profiles' used. That error message would mean he was accessing the same old original profile and the 'profiles.ini' file still existed and pointed to it. Hence the need for deleting the User Account > Application Data > 'Thunderbird' folder that contains everything.

That information on profile location does assume he has always allowed Thunderbird to create profiles in the default location. It assumes he is not using any 'portable' version of Thunderbird.

Please note: If he has more than one Windows 'User Account', then each account will contain it's own 'Thunderbird' folder containing profiles. So I would advise, he logs in to each 'User Account' and makes sure all profile 'Thunderbird' folders are deleted.

re image: As far as I can tell the settings look correct.

Check Firewall settings: After downloading and installing the 52.9.1 version of Thunderbird. Check the 'Firewall' setting as it must allow 'Mozilla Thunderbird' program. It could be a default Window Firewall or if any Anti-Virua product is installed then it could be controlling the 'Firewall'. If Firewall already says it is allowed, then uncheck it, say ok. Then access Firewall again and select 'Mozilla Thunderbird' program as 'allowed'. Just to make sure it is allowing the last version installed.

If he really has deleted all correctly, installed correct version and Firewall is allowing program. Agree with Matt - restart computer in 'Safe Mode with Networking' as this will switch off AV product that could be interfering.

re :He says he followed them, and it still hangs at checking for password. I notice the images shows lower 'Status Bar' says the email at server is 'sending secure login information'. But you/he do not mention whether the browser auto opened. Usually, the browser opens and gmail wants you enter email address and password to check you really are you. It could be waiting for a response. Is the browser opening behind the Thunderbird window and he is not aware of it?

I have shocking news. The incoming server already exists message even occurs in Windows Safe Mode with Networking. When I first took on this problem, I was like “this is going to be no sweat. That error has existed from time immemorial.” But this one has proved to be tricky.

Since it occurs in Safe Mode with networking, we tried on a different profile, but problem doesn’t exist on Thunderbird on his other more modern computers (it’s not like he’s dead in the water) or in his actual e-mail accounts, do you think it might be logical to look at Windows XP factors at this point?

I tried to use a Windows ME machine in 2007, and it was basically nonfunctional at that point, so I don’t know how much longer people can keep forcing the issue with Windows XP.

XP has not been supported for a number of releases now. What version of Thunderbird is actually being used?

I have wonderful news! I thought I had lost contact with the customer, but he resurfaced, and he got it working by: Deleting the profile in %appdata%, Switching to Offline Mode, Re-adding the Gmail accounts one by one, using the approved process using Oauth (I guess he had been using TLS before), Switching back to Online Mode.

Thank you, everyone.