I have a tribrid recorder (TRIDVR-EL16-DH) that I have configured to send email to my Gmail account on events.  It was working perfectly for months until just yesterday morning when the emails stopped.  I have not recently made any changes to the DVR or to my home network.  I tried using the email Test feature, which results in an error.  I have verified that the Gmail account credentials are correct and that the account is working, and I have tried both SSL on port 465 and TLS on port 587, but neither work.  I have a stand-alone IP camera separate from the DVR that is using the same email account credentials and SMTP settings, and is still able to send emails successfully.  I also have the 'allow less secure apps' feature enabled in my Gmail account.  I tried pinging smtp.gmail.com by DNS name and by IP address from the DVR, and am getting good replies.

I was able to capture network traffic to/from the DVR and analyze it in Wireshark.  The DVR sends a TLS Client Hello message, and smtp.gmail.com immediately responds with the following TLS message

TLSv1.2 Record Layer: Alert (Level: Fatal, Description: Inappropriate Fallback)
Content Type: Alert (21)
Version: TLS 1.2 (0x0303)
Length: 2
Alert Message
Level: Fatal (2)
Description: Inappropriate Fallback (86)

Does anyone have any ideas what might cause TLS handshaking to suddenly start failing, considering another device with identical SMTP and email account settings on the same network is succeeding?