Hi @Vinay ,
we have integrated the Active Directory/Exchange with our IAM product.
Can I understand that you have integrated an on-premises Exchange environment?
If so, I don't think you need to worry about changing the mailnikename properties .This is the "alias" attribute for a mailbox. The attribute value doesn't depend on or influence the value of DisplayName, the legacyExchangeDN or any SMTP address, so you can have pretty much any value for it, and change it as necessary excluding blank one .
In addition, the property of msexchuserculture is related to the display language of the user's mailbox .According to my test, when I modify the parameters to other language codes, the user's OWA will be displayed in the corresponding language.
Therefore, there is little correlation between the two parameters of mailnikename and msexchuserculture.
If the answer is helpful, please click "Accept Answer" and kindly upvote it. If you have extra questions about this answer, please click "Comment".
Note: Please follow the steps in our documentation to enable e-mail notifications if you want to receive the related email notification for this thread.