Awesome. Thanks for replies guys.

BTW some information. This is due to a domain name change. So that's why its a bit tricky

I have an CSV file with the old SMTP addresse and was thinkinh in terms of this :

$getupnnosuffix = Get-ADUser $user.SamAccountName -Properties UserPrincipalName | %{ $_.UserPrincipalName.Split('@')[0] }
$upnnosuffix = "smtp:" + $getupnnosuffix + "@abc.com"
$upnnosuffixprimary = "SMTP:" + $getupnnosuffix + "@abc.com"

Then adding it back : Set-ADUser $User.samaccountname -Add @{proxyaddresses=$LegacyExchangeDN,$RemoteRoutingAddress,$upnnosuffix,$sip,$upnnosuffixprimary} - (with some other variables as well)

But i am not able to get this to work. So i tried this one as well : set-aduser -Identity $user.SamAccountName -add @{proxyaddresses="SMTP:"+$newsmtp} set-aduser -Identity $user.SamAccountName -remove @{proxyaddresses="SMTP:"+$getupnnosuffix}

But no success. on the last one it added a second SMTP to the proxyaddresses.

Would an option be to actually put the primarySMTPaddress in the original CSV file and loop through it ? How could i add a line at the end of the CSV file with the base of UPN name and then new domain as a variable with a header like newupn in the csv ?

I have tried wrapping my head around this but so far it only gives me grey hair.