Hi @Tony Mourad
On Exchange side changing SAMaccountName for a user would not cause email to lose, as it is still the same AD account associated with the Exchange mailbox.
And if your default email address domain is for example contoso.com, you probably have an email address policy on Exchange to change the email domain (or have manually changed the primary email address on the mailbox) to xyz.com.
In this case changing SAMaccountName would not change the email address of the mailbox.
On Active Directory side, to my understanding and based on my test, since it is still the same AD account (same SID), it would not create new profiles on computers after the SAMaccountName change.
(While kindly note that we mainly focus on Exchange and may not be very familiar with AD)
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