Thunderbird Community Forum

My Thunderbird email account no longer lets me send out messages. I get a message error

  QUOTE____

Sending of message failed. An error occurred while sending mail. The mail server has responded. Message contains bare CR and is violating 822.bis section 2.3. Please check the message and try again.

But I am able to receive messages.

Can anyone help. Thanks in advance!!

After system complete reinstallation Ubuntu 24.04 it is not possible to send mails with SMTP Server. Receiving messages is possible!! Two fault Messages happen, I've two SMTP servers: 1. No connection to SMTP possible 2. Server timeout

And yes, I've checked nearly everything what's to find in the internet, reinstallation, change and check settings and passwords, together with the specialist from my provider. Also my provider is not able to find a mistake. As I've found out in the net, there are sometimes problems to connect to SMTP, but no solution found. Is there some security in the UBUNTU system, which blocks the SMTP connection or is this a bug from Thunderbird? Thanks in advance Andreas

bob.fannon

Feb 14, 2026, 13:01 CST

I have used Thunderbird for a number of years with Plusnet (using POP settings) in the UK. However, Plusnet has transferred their support to a company called Greenby who have made a hash of it and offer very poor support. So, I want to use Outlook as the mail server but I am unable to send any messages via Thunderbird to the Outlook server. I can however download messages with no problems. The error message I get is :- Sending of the message failed. Unable to authenticate to Outgoing server (SMTP) smtp.office365.com. Please check the password and verify the 'Authentication method' in 'Account Settings | Outgoing server (SMTP)'

My default Outgoing Sever settings are :- Server Name : smtp.office365.com Port: 587 User Name: bob.fannon@outlook.com Authentication method: OAuth2 Connection Security: STARTTLS

I have tried deleting the Thunderbird account and re-creating it but still got the same result. I also tried to use my old Icloud account ( having first setup my App Specific password) but got the same result.

Hi David This is the last attempt I did but it failed. Enclosed is the screen shot you have asked for. Keep in mind my WIN 10 has 64 Bit but the last update from Thunderbird was 32 Bit

Heinz

Thunderbird for NixOS nixos - 1.0

I could not figure out how to provide a log at all. If there is a way, please let me know and I will provide one.

Whenever I try to log in with gmail, I get stuck on this dead end:

1. Set up gmail server config (because my email ends in @vcu.edu, however I have tested this with a proper @gmail.com email and observed the exact same behavior)
2. Get propted to login with google, which works
3. Get to the "Mozilla Thunderbird Email wants access to your Google Account" page, select all and hit continue
4. get redirected to `http://localhost:35141/?state=<string of chars>&iss=https://accounts.google.com&code=<another string of chars>&scope=https://mail.google.com/%20https://www.googleapis.com/auth/carddav%20https://www.googleapis.com/auth/calendar` This page does not load, I just get a "unable to connect" error
5. get a notification stating "Authentication failure while connecting to server `imap.gmail.com`
6. get ANOTHER prompt to log in with google, exact same thing happens

please note that the port is random and is different every single time. also, google does not register that I have allowed Thunderbird access to my account, and it prompts me again every single time. Open ports: ``` sudo ss -lntup [sudo] password for jane: Netid State Recv-Q Send-Q Local Address:Port Peer Address:Port Process udp UNCONN 0 0 192.168.122.1:53 0.0.0.0:* users:(("dnsmasq",pid=2224,fd=5)) udp UNCONN 0 0 0.0.0.0%virbr0:67 0.0.0.0:* users:(("dnsmasq",pid=2224,fd=3)) udp UNCONN 0 0 0.0.0.0:33289 0.0.0.0:* users:(("librewolf",pid=185950,fd=164)) udp UNCONN 0 0 0.0.0.0:35410 0.0.0.0:* users:(("librewolf",pid=185950,fd=161)) udp UNCONN 0 0 0.0.0.0:52393 0.0.0.0:* users:(("librewolf",pid=185950,fd=218)) udp UNCONN 0 0 0.0.0.0:21027 0.0.0.0:* users:(("syncthing",pid=1850,fd=19)) udp UNCONN 0 0 0.0.0.0:54112 0.0.0.0:* users:(("syncthing",pid=1850,fd=33)) udp UNCONN 0 0 0.0.0.0:5353 0.0.0.0:* users:(("avahi-daemon",pid=1148,fd=11)) udp UNCONN 0 0 0.0.0.0:41088 0.0.0.0:* users:(("librewolf",pid=185950,fd=169)) udp UNCONN 0 0 0.0.0.0:59247 0.0.0.0:* users:(("librewolf",pid=185950,fd=132)) udp UNCONN 0 0 [::]:44815 [::]:* users:(("syncthing",pid=1850,fd=29)) udp UNCONN 0 0 *:1716 *:* users:((".kdeconnectd-wr",pid=185637,fd=15)) udp UNCONN 0 0 [::]:21027 [::]:* users:(("syncthing",pid=1850,fd=34)) udp UNCONN 0 0 [::]:5353 [::]:* users:(("avahi-daemon",pid=1148,fd=12)) udp UNCONN 0 0 *:22000 *:* users:(("syncthing",pid=1850,fd=15)) tcp LISTEN 0 4096 127.0.0.1:8384 0.0.0.0:* users:(("syncthing",pid=1850,fd=17)) tcp LISTEN 0 32 192.168.122.1:53 0.0.0.0:* users:(("dnsmasq",pid=2224,fd=6)) tcp LISTEN 0 4096 127.0.0.1:8080 0.0.0.0:* users:(("systemd",pid=1,fd=847)) tcp LISTEN 0 4096 127.0.0.1:631 0.0.0.0:* users:(("cupsd",pid=1814,fd=4),("systemd",pid=1,fd=997)) tcp LISTEN 0 50 *:1716 *:* users:((".kdeconnectd-wr",pid=185637,fd=16)) tcp LISTEN 0 4096 [::1]:631 [::]:* users:(("cupsd",pid=1814,fd=8)) tcp LISTEN 0 4096 *:22000 *:* users:(("syncthing",pid=1850,fd=21)) ```

I believe this is all the information i can provide. Firewall was disabled for testing. I cannot log into either my school or personal gmail accounts.

Thunderbird running 70-80% CPU with status bar showing. Once status bar is removed this drops. Have noticed some bug reports mentioned Linux but I'm on Windows 10 ESU (up to date). Updated TB to 153.0.3esr but no improvement. Tried troubleshoot mode but no improvement. Also noticed that emails aren't getting moved to the deleted folder from inbox. Checked today and none had been moved for 3 days. I deleted some of the older ones from 'Deleted' and then it did update.

Little thing. None of the sections seemed appropriate. Win 11 153.0.3 (64-bit) In the left-hand panel of Calendar the top left icon of the actual calendar day/week/month matrix is supposed to take you to today (though it's not obvious by the icon which changed a few versions back). When first coming to it after a restart (hibernation mostly in my case) it doesn't move the highlighted day. I have to click first on any other day, then click the icon for it to go to today.

I recently (unwisely) refreshed my WIndows 10. On restarting I had to reinstal Thunderbird. I thought I'd be able to recover all my old emails by importing the old profile from Windows.old, but I've had some problems: 1) I can't identify which profile was the most recent. 2) The info from each profile has remained on my Thunderbird, although I though it would be overwritten by the next profile I imported. 3) I've tried importing them one by one, but none of the old profiles is the one I was looking for, with all my sub folders. I need the old emails for work, invoicing and tax calculation purposes. I've now been sitting in front of my computer for a couple of days in a cold sweat, the desperation building quietly. Can anybody help?

We are facing issues with Thunderbird mail application.

Incoming emails are not being received in Thunderbird. Thunderbird is running very slowly and frequently becomes unresponsive. Sending and receiving emails is taking a long time. We have already restarted the application and system, but the issue still persists.

Kindly check the mail server settings and Thunderbird configuration from your end and advise on the necessary action to resolve this issue as soon as possible.

Your prompt support will be highly appreciated.

I am using Thunderbird Meadow.

Is it possible to send emails without a subject, other than getting the warning dialogue box.

It would be very useful.

Thank you

Hello,

I have been using Thunderbird for years without issue, but three days ago, I started having issues.

Now, I don't receive emails when I open Thunderbird. If I delete my password and re-sign in, I receive emails, but cannot send them. Trying to send an email makes Thunderbird ask me to sign in again.

I have two email accounts that I use with Thunderbird. Both accounts have this issue. I have this issue regardless of the network I'm in (work, cell hotspot, or home).

Things I have tried:

• Verified that my IMAP and SMTP settings match the guidance from email servers.
• Verified that my computer firewall is not blocking email.
• Tried connecting on different networks (so different ISPs)
• Deleted and re-entered passwords for each account

Here my current server configuration:

• Email 1 (@gmail.com)

 * Server Name: imap.gmail.com
 * Port: 993
 * Connection Security: SSL/TLS
 * Authentication Method: OAuth2

• Email 1 Outgoing Server:

 * Server Name: smpt.gmail.com
 * Port: 465
 * Authentication Method: OAuth2
 * Connection Security SSL/TLS

• Email 2 (@[university].edu)

 * Server Name: outlook.office365.com
 * Port: 993
 * Connection Security: SSL/TLS
 * Authentication Method: OAuth2

• Email 2 Outgoing Server:

 * Server Name: smtp.office365.com
 * Port: 587
 * Authentication Method: OAuth2
 * Connection Security SSL/TLS

I will greatly appreciate any help you can provide!

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.