Thunderbird Not Sending Emails: Causes and Troubleshooting Steps

If Thunderbird is not sending emails, it can interrupt both personal and professional communications. One of the reasons for this can be an SMTP configuration problem; you may have entered an incorrect SMTP server, account name or password. Other issues are related to network failures or a corrupted Thunderbird profile.

The following tutorial describes the most popular causes and easy steps to overcome the pain of Thunderbird’s failure to send emails. Additionally, if the failure is due to damage to your mailbox files, then we will tell you the optimum solution and the time to switch to another recovery technique.

Reasons Why Thunderbird Is Not Sending Emails

Prior to trying any of the workarounds mentioned here, it is crucial to comprehend the probable reasons first of all. Mozilla Thunderbird might fail in sending emails because of different causes, as follows:

• Wrong SMTP server settings
• Weak/unstable internet connectivity
• Serious authentication failure
• Firewall/antivirus interferences
• Very large attachments with emails
• Damaged or corrupted Mozilla Thunderbird profile
• Corrupted MBOX files
• Outdated Mozilla Thunderbird app

Manual Workarounds When Thunderbird Won’t Send Emails

You can try some manual workarounds when Thunderbird won’t send emails, and see if the underlying issue is settled:

1) Test Internet Connection

Stable internet connectivity is mandatory for sending your emails. So, when Thunderbird is not sending emails, try doing this:

• Open your website in a browser to verify internet connection health.
• After doing this, now restart your modem or wi-fi router if it is required.
• Then, switch to some other network to determine if the problem is related to the network.
• So, if your internet connectivity seems jittery or unstable, Mozilla Thunderbird might not connect to the outgoing email server; thus, the issue with emails not sending could occur.
• Fix this and see the results in your favour. 

2) Verify SMTP Server Settings When Thunderbird Stopped Sending Emails

Wrong outgoing email server settings happen to be a common reason for the problem of Thunderbird stopping sending emails.

For verifying SMTP settings:

• Open Mozilla Thunderbird.
• Move to Account Settings.
• Select Outgoing Server (SMTP).
• Next, do check the following info:
  • SMTP Server Name
  • Username
  • Port Number
  • Connection Security
  • Authentication Method

Try to compare all these settings with the values that have been given by your email service provider.

Also, check other related articles | Find out how to fix Thunderbird inbox not showing messages.

3) Cross-Check Login Credentials When Thunderbird Cannot Send Emails

If your email password was changed lately, Mozilla Thunderbird might still be making use of your old password. To fix this problem when Thunderbird cannot send emails, follow the steps given below:

1. First of all, remove your saved password from the Password Manager of Mozilla Thunderbird.
2. Once done with this, it is time to restart Mozilla Thunderbird.
3. Here, you have to enter the updated password whenever you are prompted to do so.
4. Wrong authentication tends to prevent Mozilla Thunderbird from sending emails.

4) Temporarily Disable Firewall/Antivirus 

Some antivirus program or firewall might be blocking Mozilla Thunderbird’s SMTP connection. You can temporarily try disabling your security software and then try sending an email to check. If that email is sent, add Mozilla Thunderbird as an exception in your antivirus/firewall settings before re-enabling your protection.

5) Repair Mozilla Thunderbird’s Folder

Corrupted folders could interfere with Mozilla Thunderbird’s functionality. To repair this, you can undertake the steps mentioned below:

1. Right-click the affected folder.
2. Select Properties.
3. Click the Repair Folder.
4. Afterwards, Mozilla Thunderbird will rebuild the folder index, which usually fixes these syncing issues & emails not sending trouble.

6) Update Mozilla Thunderbird if Thunderbird Not Sending Emails

Trying to run an outdated version might lead to several compatibility issues. To update Mozilla Thunderbird, follow the steps mentioned below:

1. Open Mozilla Thunderbird.
2. Go to Help > About Thunderbird.
3. Install any available updates.
4. Restart your app.
5. Here, updates will frequently include bug fixes as well as security improvements.

7) Start Thunderbird in Troubleshoot Mode (Safe Mode)

If the Thunderbird is still not sending emails, the issue might be with the add-on extensions, custom settings, etc. Therefore, try starting Thunderbird in Troubleshoot Mode (formerly known as Safe Mode), which can temporarily disable the add-ons and other customisations.

1. Open Thunderbird.
2. Click Help > Troubleshoot Mode.
3. Click Restart when prompted.
4. Now, click the Continue in Troubleshoot Mode button.
5. Once the Thunderbird restarts, try sending the emails.

If the emails are sending successfully, restart Thunderbird and disable recently installed add-ons one at a time.

8) Create a New Mozilla Thunderbird Profile

If your profile has become corrupted, then creating a new profile might resolve this problem. The steps are as under:

1. Close Mozilla Thunderbird.
2. Open the Profile Manager.
3. Create a new profile.
4. Configure your email account now.
5. This fresh profile would eliminate multiple configuration-related issues right away.

For more details, check the article here: repair a corrupt Thunderbird profile.

9) Send the Stuck Email Again from the Outbox

Sometimes, a persistent failed send just needs to be manually re-sent.

1. Select the Outbox folder in the left folder pane.
2. Right-click on the message that is stuck and choose Send Again, or choose File > Send Unsent Messages.
3. If it fails again, write down the exact error message you get, as it will help determine which method below to attempt next.

10) Check Message Size and Attachment Limits

Easily broken by large attachments that are well inside your providers’ limits.

Steps to deal with the size of emails and attachment limits.

1. Verify the maximum allowable size of an email attachment (20-25MB in most email services).
2. If you are sending large attachments to a recipient, consider removing attachments, compressing the attachments or instead using a cloud file sharing link.
3. Resend the message, excluding the large attachment, to see if this was the problem.

Tips to Prevent This Issue from Happening

Follow the best practices given below:

• Always keep your Mozilla Thunderbird application updated.
• Remember to regularly compact your mailbox folders.
• Do make it a point to archive your old emails.
• Always avoid saving overly large mailboxes.
• Try to back up your Mozilla Thunderbird profile on a regular basis.
• Also, verify SMTP settings after changing your email passwords.

Conclusion

When Thunderbird not sending emails, it could be due to some configuration error, a network problem, outdated software, or maybe because of corrupted mailbox files. In most such cases, manual troubleshooting helps, as we discussed here. But for more serious issues like mailbox corruption or other typical needs such as migrating emails to some other platform, the professional utility plays its part for you!