how to migrate mailbow using pop3 from exchange 2007 to exchange 2013


i have exchange 2007 servers and 2013 servers.
actually i have migrate 50% of users.

i have about 200 mailbox used only with pop3, how i can migrate them on exchange 2013 and keep the same pop3 configurtion (pop3 server and smpt server).

==> i have keep a test, i migrate one mailbox to exchange 2013, and when my application pop the mail i have this error:  Invalid login to corporate E-mail Server for username toto.

the problem dissapear if i change the pop3 server from an exchange 2007 to exchange 2013 server.

i use actually this adress for pop3:, this adress is a load balancer and this load balancer is redirected to 3 exchange 2007 cas server with pop3.

thank for help
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MAS (MVE)EE Solution GuideCommented:
You dont need to worry about that exchange will proxy the request to the right server. You just add exchange2013 CAS to the load balancer
Please read this

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cawasakiAuthor Commented:

so if i understand i just need to add to my load balancer for the exchange 2013 server and keep exchange 2007 server?

MAS (MVE)EE Solution GuideCommented:
Slowly decommission the exchange2007 servers and add other exchange2013 CAS servers to the HLB
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MAS (MVE)EE Solution GuideCommented:
cawasakiAuthor Commented:
ok, but i am not sure if i keep exchange 2007 and 2013 on load balancer, it will not work, because if one mailbox on exchange 2013 use a pop3 server on exchange 2007, it will not work. i have test this:

an exchange 2013 mailbox, pop3 server an exchange 2007  ==not work
an exchange 2007 mailbox, pop3 server on exchange 2013 == work.

i think i need to use only exchange 2013 pop3 server for both exchange 2007 and 2013 mailbox??
MAS (MVE)EE Solution GuideCommented:
You interface should be Exchange2013. All your request will get proxy to Exchange2007.
But it will not work externally . It will work only internally
cawasakiAuthor Commented:
hi, ok thank you all my pop3 client are internally, so i will redirect all pop3 request to exchange 2013 and it will proxy them to exchange 2007 when mailbox is on exchange 2007 server.
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