How to provision Office365 accounts with domain.onmicrosoft.com as secondary SMTP address?
1- Go to Find Domains section in Migrator for Notes to Exchange (MNE)
2- Click Add Domain button
3- Type domain.onmicrosoft.com
4- Click OK
5- Go to Export Notes Directory section in MNE
6- Click Export Directory button
Above process will allow you to add firstname.lastname@example.org as secondary SMTP address to the provisioned Office365 users.
You need to change domain to the domain you see in your Office365 accounts such as email@example.com to firstname.lastname@example.org