Hi @Glenn Maxwell ,
is it possible to achieve this using transport rule. in one transport rule i want to add 100 users like the below as i cannot create 100 rules.
Not possible to include all the 100 users in one transport rule, so if you want to achieve this using transport rule, you will have to create 100 rules, one for each user. This is however not practical at all.
******@consoto.com doesnot have a valid mailbox or license.
Since ******@contoso.com doesn't have a mailbox, configuring email forwarding for them as suggested by Andy isn't not applicable either in your scenario, because Email forwarding requires that the from account has a license unless it is a shared mailbox, see this link.
Taken in the round, if you don't have any specific need to sync @contoso.com from AD to Azure AD, I‘d suggest stopping them(@contoso.com) from syncing to AAD by means like moving these AD accounts into a different OU which is excluded from the AAD sync. Then you can bulk add the ******@contoso.com addresses as an email alias for ******@contoso.com using PowerShell script.
Another thought is to bulk create "******@contoso.com" as shared mailboxes which don't require licenses, then you would be able to enable mailbox forwarding for them in bulk through Exchange Online PowerShell script.
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