1-) I use exchange 2010 server. there are some accounts on it.  I want to update email addresses using exchange management shell. I tried a command "set-mailbox -identity accountname -PrimarySmtpAddress new@domain"

But that leaves old email address as secondary whereas i wish to replace it.

how can i do that ?

2-) there is a domain has many accounts on the exchange server 2010 .

the domain is going to move soon to outside email server which is unix based. During the migrate, those accounts moving domainname need to be left for a while  in case those users can reach to their old accounts.

During the move ( such as changing MX dns operations), Sending mails other domains in the exchange server need to reach to new outside mail server.

Which configurations need i do on the exchange server ?    

Hi,

Q1: Run the following command. The second command will remove other email addresses.

set-mailbox -identity accountname -PrimarySmtpAddress new@domain

set-mailbox -identity accountname -EmailAddresses new@domain

Q2: If exchange 2010 can coexist with the email server which is unix based. Before moving the mailboxes, these accounts will use the old domain name. Because I dont understand that email server which is unix based, so I cant provide more advice, sorry.

Best Regards.

the command 'set-mailbox -identity accountname -PrimarySmtpAddress new@domain'  changes PrimarySmtpAddress  but old primarysmtpaddress leaves as secondary.

I only want to change/replace concerning address without leaving or removing at its address list. 

is not there any commands about that ?