We have Zoho One and use Zoho mail with our own domain. One user is unable to forward email messages she receives from third parties to another user. These email messages disappear into the ether and do not appear in her Sent folder. Several days later she gets an email message saying the mail was not delivered.

The forwarded messages were failing to be sent, and then several days worth of the Undelivered messages came through at the same time on September 21.

I have triple-checked the configuration and can find nothing wrong.