• Does Thunderbird work as expected in Thunderbird troubleshooting mode?
• Does Thunderbird work as expected with your OS started in safe mode with Networking. Instructions for each operating system: Windows 10/11, Windows 8, Windows 7, OSX

I tried running TB in troubleshooting mode but there was no change in TB, still hangs with the message "checking mail server capability". I also tried running Windows 10 in safe mode but then when I open TB it said there was no network connection. Maybe I didn't click on the safe mode with network links or something like that. I don't know whether this is a problem in Thunderbird, the mail server (I'm using Deluxe APlus which I have used for about 15 years), or with Windows 10. I don't even know what the message means "checking mail server capabilities". Is there someone that can fix this for me? At the moment it has made TB not usable on my PC, since I can't receive any e-mails. The problem just popped up suddenly several days ago.

re : I also tried running Windows 10 in safe mode but then when I open TB it said there was no network connection.

You would need to use 'SAfe Mode with Networking' and if you normally use wireless connection then you will need to use an ethernet cable to connect to router.

This is the best method of checking whether another program is causing a problem when Thunderbird tries to connect to server.

At this point we do not know anything about your setup. Please post the following information: In Thunderbird Help > Troubleshooting Information Scroll down to 'Mail and News Accounts' section Copy all the data and post the info into this forum question.

I've seen this 'Check mail server capabilities' occur in the past when people were using a server which was not using up to date tls security. I've also seen issues when people were using STARTTLS instead of SSL/TLS. So post the info stated above so we have a starting point.

re :the mail server (I'm using Deluxe APlus which I have used for about 15 years),

Have you got your own website? Do you mean you use web host 'APlus.net' ?

What version of Thunderbird are you using ?

To : Todd-Hall

Thanks for providing your insights on how to diagnose my problem. As an additional bit of info, I did a test sending an e-mail, which returned the following message but did get sent:

Your message was sent but a copy was not placed in your sent folder (Sent) due to network or file access errors. You can retry or save the message locally to Local Folders/Sent-yjhuang@whiteboxtechnologies.com.

Here is what the Mail and News Accounts section of the Thunderbird Troubleshooting page says. I did a cut and paste which lost all the formatting. I hope the information is still readable.

Mail and News Accounts ID Incoming server Outgoing servers Name Connection security Authentication method Name Connection security Authentication method Default? account1 (imap) imap.whiteboxtechnologies.com:143 STARTTLS Normal password smtp.whiteboxtechnologies.com:587 STARTTLS Normal password true account2 (none) Local Folders None Normal password

I have a web site at www.whiteboxtechnologies.com since 2007 that's hosted by APlus.net.

My Thunderbird is Version 115.12.2, downloaded in December 2023.

As far as using an ethernet cable to test running Windows in safe mode, that would be difficult because my computer is downstairs and would need a 50-75 ft long cable to reach the router. When I tried to run Windows in safe mode, I selected it with networking (Option 5) but still it said there was no internet connection. Of course I could move my PC and monitor upstairs but that would be a hassle.

Many servers that have sent mail passed through them will auto put a copy in the webmail sent folder eg: gmail. So an imap account will have it saved by default. In your case this may not be something that occurs. As you have an imap mail account can you perform some checks.

In Folder Pane:

• Right click on the name of the account folder and select 'Subscribe'
• Click on 'Refresh' button
• Select the 'Sent' folder and click on 'Subscribe'
• Click on 'OK'

• Now right click on 'Sent' folder and select 'Properties'
• click on 'General Information' tab
• select checkbox - Include messages in this folder in Global Search results
• select checkbox - When getting new messages for this account, always check this folder
• Select 'REtention Policy' tab
• Select 'Use my account settings
• Select 'Don't delete any messages'

• click on 'Synchronisation' tab
• select checkbox 'Select this folder for offline use'

In Account Settings:

• Select 'Copies & Folders' for the account

When sending messages, automatically:

• Select checkbox : 'Place a copy in'
• Select : 'Other'
• Choose 'Sent on mail account name'

• Select 'Synchronisation & Storage' for the account
• Click on 'Advanced' button
• Expand the drop down for the mail account to see list of folders
• Check the 'Sent' folder has a tick in the box in 'Download' column.
• Whilst in that location - if you want a full copy download then make sure each folder has a tick to show it has been selected for download. Otherwise only headers get downloaded.
• Click on 'OK'

Exit Thunderbird to ensure all settings are properly updated to all various files.

Whilst Thunderbird is closed. Please check your Anti-Virus. Ant-Virus products are well known for causing some issues because they can scan any file that gets opened or scan files that get received and sent. If the Anti-Virus has got control over a file then Thunderbird cannot use it. I would advise you set up an exception for your Thunderbird profile folder to not scan this folder or it's contents. Also check to see if you have a setting which is auto scanning outgoing mail and switch it off.

If you have other similar products eg: malware, CCleaner, Wisecleaner etc Please make sure they have no access to Thunderbird profile folder or it's contents. Set up an exception if required.

Start up Thunderbird and wait for all auto connections with server to be performed - if possible wait until you have received some emails before attempting to send. Select the 'Sent' folder to make sure it has sycnhronised with server. Then attempt to send.

If you had been able to use 'Safe Mode with Networking' using ethernet cable then this would have temporarilly disabled the Anti-Virus and other non required programs properly - it's a useful tool for checking to see if there is any interference from programs.

I understand your predicament with router in one location but computer (not laptop) set up elsewhere. I have internet to front of house which is where the socket is located. But then I put an extension into socket and run cable under floorboards to the back of house and connect to a splitter socket which has the cable that connects to router. Then I have ethernet cable from router across room to computer. I normally operate via ethernet, but I can swap to wireless if necessary.