Merge two Office 365 accounts same tenant different domain

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I wanted to know if there is a way via powershell or Office 365 UI admin portal to merge two Office 365 accounts into one. Both accounts are under the same tenant but have two different email domains. Want to ensure mailbox and calendar are not lost.

Example: Tenant costco@com
old Domain1: Ventrial@.com
New domain1: Coscto@.com

3 Replies
There's nothing built-in for this scenario. Manual export/import is your only option.
You can use IMAPSYNC to symplify this task
@Anon121 you can use bititan tool to migrate your old domain 1 mailbox to your new domain 1 mailbox along with the calendars

https://help.bittitan.com/hc/en-us/articles/360042885254-MigrationWiz-Mailbox-Migrations