While migrating from Zimbra you noticed following error in your logs:
“Fatal error during migration process: Failed to authenticate:A connection attempt failed because the connected party did not properly respond after a period of time, or established connection failed because connected host has failed to respond”.
The Zimbra server blocked the connection. Most probably there are some security restrictions configured (firewall, server settings, IP restrictions).
Make sure that there is no any restrictions configured (firewall and proxy settings).
If needed, please contact our support team at firstname.lastname@example.org to get an IP to authorize it in your infrastructure.