Gmail issue adding external email account to send.

[dbeato]

While helping a customer add their email account to Gmail to be able to send emails we got the error as below:

Background on how to Setup External account to send
https://support.google.com/mail/answer/22370?hl=en

Error
"TLS Negotiation Failed. The certificated doesn't match the host., code: 0"

Resolution
The email server had the correct SSL Certificate but still was having an issue. In this case this was an Exim server and it had a correct SSL Certificate. For the heck of it ran the SSL Checker on https://www.sslshopper.com/ and it came all good with the whole SSL Chain.

However when I ran the scan with https://www.checktls.com/TestReceiver and found an issue with the SSL Chain.

Once I fixed the SSL Certificate (By adding the Intermediate and Root Chain) it worked. The Dovecot SSL on the same server had the chain so that was easy.

Found also this https://gucia.pl/2020/04/tls-negotiation-failed-the-certificate-doesnt-match-the-host-solved/