Thunderbird Community Forum

so anyone who known this when you check your Email why does it take so long for the check to fail! So I went looking for a fix and found it in advanced preferences

mailnews.tcptimeout set to 100 over a minute wait thats just wrong so set it to 5

Today, November 12 2026 I lost all access to Microsoft email accounts (through TB) and calendars (through TbSync). Nothing, neither business or personal email accounts, will send or receive email as of this moment. I have checked behavior of software in troubleshoot mode and nothing changes. I have not located an error log in TB. My only indication of a problem is that the windows error console alerts an error "server graph.microsoft.com responded with an error" No other information. It would be nice if the error logs were easily available in TB.

Is there a general conflict between MS graph server and TB??

It was working fine on the new computer until yesterday. Now I get a pop-up box that says: ' Unable to connect The connection was refused when attempting to contact localhost.

The site could be temporarily unavailable or too busy. Try again in a few moments.

If you are unable to load any pages, check your computer's network connection. If your computer or network is protected by a firewall or proxy, make sure Thunderbird is permitted to access the web.

This is mostly informational for the community and a question

Background - I was affected by the missing intermittent mail at version 159. After the release of version 160 my problem persisted. Following the fix I set about more troubleshooting. I Had only issues with one of four email accounts tn TB, one other account is to a different server but has the same setup port 993 SSL/TLS setup. My email provider has great support and indicated many had had issues and the reports of 160 correcting the problem were many.

I found an ESET setting was the culprit, in advanced settings under "email client setup" they have a toggle for "Scan IMAPS mail transport" by default this is on. After switching this off version 160 works perfectly. This function has been in place a while and can confirm it worked OK with version 158.

I do not think its the vendor, as in one of my test I loaded the affected account into Windows 11 Outlook and established instant sync with "Scan IMAPS mail transport" on. The problem only effects TB sync with IMAP on one server.

From ESET's information this function scans the mail in route to the client. It does not affect "other" AV function with mail.

The Question: Should I pursue resolving this with TB? Or is it just a conflict?

I run an old imac with ventura 13.7.4, mostly i use my email prog from my server, but i can't get links etc. When i switch to Thunderbird, much of the time thunderbird just sits there, saying it's connecting, but it's not. i will dump it soon and try something else, i think. Sometimes it works.

I think i am running TB 159.0. I haven't the faintest idea how to access the TB app menu, but this is what it says on my app menu.

I can't upgrade my OS, it's a miracle this thing works at all any more. Yay for old geeks!

After many years I have recently been receiving intermittent server refusals, as many as 12 to 15 per day, on mail.twc.com with Spectrum. After confirming incoming and outgoing server settings, Spectrum advises that the problem is with Thunderbird.

TB is not downloading pop3 emails again.

What does this mean?

NetworkTimeoutError: a Network error occurred Pop3Client.sys.mjs:380:18 SecurityError info: Pop3Client.sys.mjs:440:20 SecurityError cert chain: legacy.pop.mail.yahoo.com; serial# 07:CF:5F:D8:B7:96:17:C0:9F:C0:58:12:90:5A:41:8F <- DigiCert Global G2 TLS RSA SHA256 2020 CA1; serial# 0C:F5:BD:06:2B:56:02:F4:7A:B8:50:2C:23:CC:F0:66 <- DigiCert Global Root G2; serial# 03:3A:F1:E6:A7:11:A9:A0:BB:28:64:B1:1D:09:FA:E5 Pop3Client.sys.mjs:445:22

A timeout in the connection to the server means that I can neither receive nor send emails, even though this had been working until today. I'm working on the latest windows version. How to solve this problem?

Hello; I'm having connectivity problems with the TWC ports. They are the correct ports as per their CS and said that it could be an issue with Thunderbird connecting to the ports. I was hoping to test them at this support site but there isn't any help except historic forum responses, which I don't know will be of help. I'm using Google to open the mail. Any ideas out there?

The DELE command did not succeed. Error marking a message as deleted. Mail server pop.mail.yahoo.com responded: Too many requests.

When trying to launch Thunderbird it gets stuck on "connecting to imap.comcast.net". App Version 102.0.1 GRE Version 102.0. Windows 10 on home laptop. I tried launching in safe mode and got the same thing

Over the past few days, the format for emailing seems to have changed on my PC, an error message keeps coming up saying: Error occurred connecting to imap.talktalk.net, I have tried to follow Google advice but it doesn't seem to have made any difference, I can still send and receive emails, but have to wait for all my old emails to load before I can do this, I'm a novice and a pensioner, please help Thank you

I am running Windows 7 Pro (64 bit, Quad Core) on a desktop. Latest Firefox v. 115.44.0esr (64-bit). Latest Thunderbird v. 115.18.0 (64-bit). No VPN (but worked before). Security settings "off" (I have checked and checked -- hours and hours.)

I have been having Thunderbird email authentication errors for months -- but suddenly now all the time. Can't log on to ISP email account (but I can in the browser). "Non-overridable TLS error occured." I have an Arch Linux desktop with Firefox -- works fine. The Arch Linux Thunderbird works fine.

This sucks. Time to change browser and email client? Please advise.

D. Stewart

1. 1. Thunderbird connects to my IMAP/SMTP server but neither receives nor sends mail

I am having a problem with Thunderbird on Windows with a custom-domain email account hosted by Advika Web.

1. 1. 1. Account

Email address: `connect@synergyappstudio.com`

Mail hosting provider: Advika Web

The mailbox and password are confirmed to be valid because I can successfully log in to the provider's webmail using the same email address and password.

1. 1. 1. Server settings provided by the hosting provider

Incoming IMAP:

• Server: `mail.synergyappstudio.com`
• Port: `993`
• Connection security: SSL/TLS
• Authentication: Normal password
• Username: `connect@synergyappstudio.com`

Outgoing SMTP:

• Server: `mail.synergyappstudio.com`
• Port: `465`
• Connection security: SSL/TLS
• Authentication: Normal password
• Username: `connect@synergyappstudio.com`

1. 1. 1. What happens in Thunderbird

Thunderbird shows:

> Connected to mail.synergyappstudio.com

However, incoming messages are not downloaded and outgoing messages cannot be sent.

The SMTP error I received was:

> The connection to Outgoing server (SMTP) mail.synergyappstudio.com timed out.

1. 1. 1. Connectivity tests

I tested the server from Windows PowerShell.

Port 993:

`Test-NetConnection mail.synergyappstudio.com -Port 993`

Result:

> RemoteAddress: 103.69.196.146 > RemotePort: 993 > TcpTestSucceeded: True

Port 465:

`Test-NetConnection mail.synergyappstudio.com -Port 465`

Result:

> RemoteAddress: 103.69.196.146 > RemotePort: 465 > TcpTestSucceeded: True

Therefore, both TCP ports are reachable from my computer.

1. 1. 1. TLS tests

I also tested the actual TLS handshake rather than just TCP connectivity.

TLS 1.2 against IMAP 993 failed with:

> Unable to read data from the transport connection: An existing connection was forcibly closed by the remote host.

TLS 1.0 against IMAP 993 produced the same result:

> Unable to read data from the transport connection: An existing connection was forcibly closed by the remote host.

I also tested the TLS handshake against SMTP 465 and received the same "connection was forcibly closed by the remote host" result.

1. 1. 1. Comparison with Outlook

There is an important comparison:

The same mailbox **successfully connects and authenticates in Classic Outlook** using the same server and credentials.

However, I am using Microsoft Office Home & Student, so Classic Outlook is not available to me as a practical permanent solution for this business email account.

Microsoft's **New Outlook** also fails to add the account and displays:

> Sign in failed. Please try again in a few minutes. You may need an app password.

The mailbox does not use Microsoft 365 authentication. It is a conventional hosting-provider IMAP/SMTP mailbox.

1. 1. 1. Thunderbird troubleshooting already attempted

I have:

• Confirmed the password works through webmail.
• Confirmed the supplied IMAP/SMTP server names.
• Confirmed ports 993 and 465 are reachable.
• Confirmed SSL/TLS settings.
• Used Normal Password authentication.
• Used the full email address as the username.
• Tried Thunderbird with the supplied IMAP/SMTP settings.
• Reduced **Maximum number of server connections to cache** from the default 5 to 3 and then to 1. This did not resolve the problem.
• Restarted Thunderbird after changing the connection-cache setting.
• Tried Thunderbird's connection logging, but the generated log files remained 0 KB, so no useful log was produced.

1. 1. 1. Additional observation

Thunderbird displays "Connected to mail.synergyappstudio.com", but the account does not actually synchronize incoming mail.

The provider's webmail works normally, and Classic Outlook works with the same mailbox.

1. 1. 1. What I would like help determining

Could you please help determine whether this is:

1. A Thunderbird IMAP/SMTP compatibility issue with this particular mail server; 2. A TLS negotiation issue; 3. A Thunderbird configuration/profile issue; 4. A Windows/security-software interaction; or 5. Something specific to the mail server's IMAP/SMTP implementation?

In particular, I would like to understand why Thunderbird can establish the connection but cannot complete the IMAP/SMTP communication, while Classic Outlook works with the same server, ports and credentials.

I can provide Thunderbird version information, Troubleshooting Information, screenshots of the account configuration, or any additional diagnostic information you need.

I'm not sure at which point this behaviour started, it was either after thunderbird suggested that I compacted my folders or perhaps after the update to the latest Thunderbird version. Sometimes when I start Thunderbird I only get the inbox (which is empty) . Sometimes I get nothing then the inbox gets downloaded from my IMAP account. Sometimes I see all my folders for a few tenths of a second and I see message on the bottom border (where it normally talks of connection to the mail server) but these messages talk of deleting all my folders one by one. On one occasion all my folders were laboriously downloaded one by one (as reported on the bottom line.) Often shutting down Thunderbird and opening again results in all the folders being instantly available (so they must have been there all the time). It sometimes takes a number of shutdown/restart cycles to get the email folders back. Any ideas what is going on and how I can stop it happening? Thank you for getting this far.

Cannot send or receive email all of sudden in Thunderbird. When I the click the messages icon, nothing happens, and I get "Could not connect to server mail.twc.com; the connection was refused". When trying to send a m,message I get "Sending of the message failed. The message could not be sent because connecting to Outgoing server (SMTP) mail.twc.com failed. The server may be unavailable or is refusing SMTP connections. Please verify that your Outgoing server (SMTP) settings are correct and try again." No settings were changed and everything was fine when I put the computer to sleep. This happens on both a Win 7 and 11 machine Email is a Time Warner (now Spectrum) Road Runner account (twc.com). Spent an hour with Spectrum, and they say this is a third party (Thunderbird) issue. A friend has the same setup, and is having the same problems that started at the same time. Win 11 version 150.02 Win 7 115.18.0 (latest available for win 7)

Appreciate any help....