SMTP sending fails in thunderbird

SMTP sending fails in thunderbird, Dial 1-855-785-2511 for support

Hello!

When trying to send an email  you get the error
“Sending of the message failed.

Example 1

The message could not be sent because the connection to Outgoing server (SMTP) smtp-mail.outlook.com timed out. Try again.”
I used Outlook 2010 and switched to Thunderbird since I got a similar error with Outlook. Till three weeks ago everything was working fine.

I get this with a regular outlook.com account (automatic account setup through Thunderbird) and a custom domain zoho.com account with manual configuration (port 587 and 465).
Getting email through IMAP is no problem.
I use Win 7 and the latest Thunderbird. I uninstalled PandaAntiVirus,  and other antivirus program but that did not help.

What possible fix  Solutions 

1.

Moving to Thunderbird Support as no bug has been identified here.

What is security software running on that system?
Have you set the anti-virus software to NOT scan outgoing messages?
What specific settings are selected in Thunderbird for the SMTP server for that Outlook account, including server name, port number, and choices for “Connection security” and “Authentication method” under Tools>Account Settings>Outgoing Server (SMTP) (at the bottom of the list of accounts on the left)>*server*>Edit?

2.

I am having this exact same problem as has been described above.

It is happening on two different computers, both running Thunderbird 38.4.0 on Linux. Both computers are configured with 3 or 4 different email accounts (a different set of accounts on the two different computers), and the problem is the same on all email accounts on both computers.

The problem started recently (couldn’t say exactly but it seems like a few weeks at the most).

The nature of the problem is exactly as the others have described and through extensive testing seems to be very consistent. Here’s how it is:

Receiving email works just fine. The problem is with sending email.

Short messages with no attachments send fine with no problem. But add any but the smallest of attachments (anything more than a few kb in size), and it won’t send, giving an error message instead. Also, make the message text very long, and it gives the same error message.

This is the text of the error message:

“Send Message Error
Sending of the message failed.
The message could not be sent because the connection to the Outgoing server (SMTP) [the server name, whatever it is, e.g. mx01.kolabnow.com, smtp.comcast.net, or whatever] timed out. Try again.”

Most of these email accounts are using port 587, STARTTLS, Normal Password. I really think it has nothing to do with the server or server settings because it’s the same problem with 7 different email accounts on 5 different servers on 2 different instances of Thunderbird on 2 different computers, and I made no changes to any of the settings prior the start of the problem.

I am also not using any type of antivirus software so this is clearly not the problem.

Really looking forward to getting this solved and will greatly appreciate any help that anyone has to offer.