Authentication failed, code: 550

Getting Started
#1

I can no longer connect Gmail to my smtp web server and get the following error which means I cant send out emails with my domain name:
TLS Negotiation failed, the certificate doesn’t match the host., code: 550

The username and password are definitely correct as I can login to the email server directly. Mx records are bypassed and have worked for some time. I tried both TLS and SSL and it either says cant connect or it reports the certificate issue. To try and get things working, I added a bypassed Mail A record. Here are my DNS records

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#2

I’m a little confused what you mean by “smtp web server”

Adding the bypassed mail subdomain is the right thing to do. The Cloudflare proxy will not pass SMTP traffic.

What happened when you tried to point Gmail to the un-proxied mail.vizguard.com name? Was that subdomain proxied before, and if so, did you wait at least 5 minutes after un-proxying it before trying to test?

Also, does the certificate on the server actually include “mail.vizguard.com”, either explicitly or via a subdomain wildcard?