@sharif I figured out a workaround to a bug in Carbonio. zimbraMtaSmtpCnameOverridesServername no This set to no should allow CNAMEs to work ( i...

I was able to achieve this with the following (apache reverse proxy): <Location /carbonio> ProxyPreserveHost on ProxyPass ProxyPassReverse&l...

To add to this: The reason this did to work for me was that I'm us in-v3.mailjet.com as a relay which is a CNAME for in.mailjet.com. This should not...