I am trying to send emails through thunderbird to our old exchange email server.

This was working till I recently updated thunderbird 78.

I get the following message

Sending of the message failed.
Peer using unsupported version of security protocol.
The configuration related to exch1.email.server.somedomain must be corrected.

This was fixed by changing the support version of the TLS protocol.

The default has changed to TLS version 3.

In Linux I go to:

  • Edit
  • Preferences
  • General
  • Scroll all the way to the bottom
  • Config Editor button
  • I accept the risk
  • search for security.tls.version.min
  • change default to what ever your server supports

I used the following to check what the server supported

openssl s_client -starttls imap -tls1  -connect exch1.email.somedomain.com:143 | grep 'New,'
New, TLSv1.0, Cipher is ECDHE-RSA-AES256-SHA

Unfortunately, there are not other supported versions

openssl s_client -starttls imap -tls1_3  -connect exch1.email.newsclip.co.za:143 | grep 'New,
New, (NONE), Cipher is (NONE)

Will need to send the admins a stern email telling them to patch and upgrade. We will actually migrate to something that is not an MS product.

For more info checkout

  • 2
    Note that the option uses TLS "protocol" numbering, which is off-by-one from the "marketing" numbering -- that is, the new default of '3' actually sets the minimum to TLSv1.2 i.e. -tls1_2 (which has been the primary choice for the last few years). It's quite normal that your server doesn't support TLSv1.3 as it's very new, but your admin really ought to upgrade it for TLSv1.2 at least. – user1686 Nov 19 '20 at 12:36
  • 1
    Windows Server supports TLSv1.2 as far back as 2008 R2, so how old is your Exchange version, 2007? – Neil Nov 19 '20 at 21:59

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