Cannot send mail

If you've followed instructions for configuring Thunderbird and still cannot send mail for one or more of accounts, the following may help:

Basic troubleshooting

Firewalls and antivirus software

Verify that your firewall or antivirus program is not blocking Thunderbird. If you recently upgraded Thunderbird, verify that the firewall is not blocking the new version.

Offline mode

Verify Thunderbird is in online mode, not offline mode: click "File -> Offline"; "Work Offline" should be unchecked. If you send a message while in offline mode, it goes to the Unsent Messages folder in Local Folders. See below for Advanced tips.

Outgoing mail settings

First, get the correct outgoing mail (SMTP) settings from your service provider, usually your Internet Service Provider (ISP): try their website, search Google for your ISP plus the word "smtp", or call them.

Verify the settings in Thunderbird exactly match what your ISP provides: no typos (e.g., "smpt"), extra spaces, punctuation mistakes (e.g., no commas instead of periods) or capitalization errors (e.g., lowercase instead of Caps).

Click "Tools -> Account Settings -> Outgoing Server (SMTP)" (at the bottom of the left pane—you may need to scroll down), and double-check:

• Server Name

• Use name and password: Your username might be your full e-mail address (e.g., "johndoe@domain.com") or only the part before the "@" ("johndoe"), depending on your service provider. Also, try unchecking this box; your e-mail service provider might not support it.

• Use secure connection: Unless your service provider supports SSL connections for outgoing mail, select "No".

• Port: Some service providers use non-standard ports (25 is standard). If you're having problems, ask them which ports they support for SMTP or outgoing e-mail.

• (For help with multiple servers, see Advanced tips, below.)

Also, click "Tools -> Account Settings -> [account name] Server Settings -> Advanced -> SMTP" and verify the correct SMTP server is selected there. If you see "Relay access denied" or "Relaying denied" errors, be sure to verify this setting.

For advanced users

• If you installed Thunderbird without Offline Support: Close Thunderbird and go to your profile folder. Back up the "prefs.js" file, then open it with a text editor (e.g., Notepad) and delete only the line containing the "network.online" preference. (Be careful editing "prefs.js"; if you make a mistake—you'll notice many settings changed when restarting—close Thunderbird and restore the backup copy.)

• For a non-default/secondary outgoing server: go to "Tools -> Account Settings -> Outgoing Server (SMTP)", then click "Advanced", select the appropriate server, and click "Edit".

• Follow these instructions for logging and advanced troubleshooting. (The log will include your username, password and possibly other private information, so be sure to remove the private info if you send the log to anyone else.)

ISP's blocking port 25

In an effort to stop spam, many ISP's (Comcast, Cox, many others) block all traffic to port 25 on anything except their own SMTP servers. This plays out like this:

Say you configure your laptop's Thunderbird's "Outgoing Mail Server" to use smtp.mycompany.com port 25. When you test sending e-mail, it works, because you're not subject to Comcast rules on your company's network.

Now take the laptop home and try sending mail. Everything looks normal, no errors or anything. But that mail simply vanishes. Comcast drops it because it was addressed to port 25 and not to Comcast's SMTP server.

The fix is simple but may not work for all servers. In Thunderbird's "Outgoing Mail Server" panel, replace the default 25 with 587. RFC 2476 explains why this works for newer SMTP servers. (For sbcglobal.net, the fix is to change port to 26.)

If this doesn't work, it may be possible to solve this with ssh tunnels and/or router changes. (If you work out the details, please update this article accordingly.)

You can receive mail but can't send it

The symptoms are these: You carefully compose an outgoing e-mail message, hit "Send" and up comes a window asking for your username and password. ("Hmmmm", you think, "I already told Thunderbird about these....") You enter the desired info, tell Thunderbird to remember them and hit "Send" again. After a pause of a few seconds, back comes that same window. After several repitions of this, you cancel the send, and up comes an error window telling you that your SMTP server is down or some such. A check of my system shows that sendmail is working just fine and that you can send outgoing messages, just not with Thunderbird.

The fix is to go to "Edit -> Account Settings -> Outgoing server(SMTP)" and turn off your name and password. You ISP's server does not require these, and it is confused when it gets them.