Update and then..Sending of the message failed! Peer using unsupported version of security protocol.
just updated mozilla email and got this message : Sending of the message failed. Peer using unsupported version of security protocol. The configuration related to smtp.EMAILPROVIDER.com must be corrected
Opaite Mbohovái (1)
This may be because the server only supports TLS 1.0 or 1.1, whereas TB 78 requires a minimum of TLS 1.2. This is reflected in the preference security.tls.version.min default setting of 3 in Options/General/Config. editor. Right-click the pref., Modify, and change it to 2 and see if it helps, or 1.
http://kb.mozillazine.org/Security.tls.version.*
It could also be due to an antivirus program interfering if it's scanning secure connections.