Zimbra: MTA rejects mail
Had configured my Zimbra MTA to use TLS. When using a new email client on my Windowsphone 8 operating system (yeah yeah, it’s my mobile for my job, I didn’t chose it myself) I was not able to send email via TLS and accepting self-signed-certificates. So… I had to disable TLS authentication only to be able to send email again from this client from an external network.