Below mail servers have been migrated
mail3
mail6
mail7
All users are suggested to use SMTP authentication with port 587 for SMTP to avoid blacklist check on their IPs.
We have a few reports of bounces for addresses that are newly created on the new servers, but DNS is sometimes hitting old servers, so the newly created address is returning.
This will resolve with propagation but we are also working to resolve it sooner as well. This is a new measure to prevent spam that happened last time by being more selective with mail that is allowed through.