https://support.mozilla.org/en-US/kb/cannot-send-messages

I tried all that. Multiple times. Nothing has worked.

Try sending while in your operating systems safe mode:

• Restart the operating system in safe mode with Networking. This loads only the very basics needed to start your computer while enabling an Internet connection. Click on your operating system for instructions on how to start in safe mode: Windows 8, Windows 7, Windows Vista, Windows XP, OSX

If safe mode for the operating system fixes the issue, there's other software in your computer that's causing problems. Possibilities include but not limited to: AV scanning, virus/malware, background downloads such as program updates.

Mail went through when I was in the safe network mode. Thank you, Matt!

Now... how do I track down what is causing the problem? The other email addresses I use are able to send just fine. Why would one thing be stopping one email smtp, but not the other?

I'm so confused.

WOOHOO!

I restarted Thunderbird with the add-ons disabled. Lo and behold, email sent without a problem. So, I tested and added each add-on back, one at a time, to see if I could determine the culprit.

It was my readnotify read receipts! I had not added this email address to the list of emails to use and it was blocking the send. Now it's added and the email is working.

Thank you again, Mozilla peeps, for your assistance!

I have the same problem (all of a sudden).

Send Message Error:

Sending of message failed. The message could not be sent because the connection to SMTP server smtp.mail.me.com timed out. Try again or contact your network administrator.

They send with Mac in safe mode ok. I've disabled all plug-ins and it still doesn't work.

This happens to both my email accounts. My 'iCloud' account and my own domain account.

Any help gratefully received..

Rick, it would have been better for you to ask your own question. But in the interest of getting things done, try disabling any anti virus you have and see if that helps.

Thanks but I'm not using any anti-virus..

 Yosemite OSX 10.10.2
 MacBook Pro (Retina, 15-inch, Early 2013)
 Processor Name:	Intel Core i7
 Processor Speed:	2.4 GHz
 Number of Processors:	1
 Total Number of Cores:	4
 L2 Cache (per Core):	256 KB
 L3 Cache:	6 MB
 Memory:	8 GB
 Boot ROM Version:	MBP101.00EE.B07
 SMC Version (system):	2.3f36
 Hardware UUID:	3D6713F9-F271-5658-93F7-A3D0888467E0

It would be more likely to be extensions blocking sending, not plugins.

I don't (apparently), have any add-ons or extensions installed just 11 plug-ins. All disabled.. Thanks.

After numerous configuration attempts over the last few days, my iCloud AND own domain email accounts finally work. Sadly I don't even know what I did to maybe help others but obviously a combination of settings solved it.

I've re-activated all 11 plug-ins in Thunderbird an email's still working, so not that then..!

Thanks for all your help everyone!!

Rick

News Flash!

I think through just luck, yesterday I managed to enter the correct settings in Thunderbird for my email to work. (Images of settings below) - All emails were coming in and going out fine.

This morning, same problem's back. I can receive but can't send. I haven't touched anything at all or downloaded anything. I haven't even used my computer!

Ther MUST be a serious issue with Thunderbird...

Or a problem with the server.

How do you post a question on this forum? It keeps sending me round in circles offering questions I don't want to ask!

I want to post my problem in the Thunderbird section and not ask a question Mozilla suggests for me!!

Unuser-friendly forum. I think I've set myself up as a 'contributor' and not a regular punter!!

Any help please..!!!

I have found that I have to use a non-Mozilla browser to ask questions on this forum, so I use Safari. Mozilla browsers are fine for answering questions here, but not for asking.

Thanksfinitarry said

I have found that I have to use a non-Mozilla browser to ask questions on this forum, so I use Safari. Mozilla browsers are fine for answering questions here, but not for asking.

Well that doesn't give me much faith about Mozilla's products. This is really a strange forum.. Maybe I should've ditched Thunderbird on day one!!