TCP Ports for Exchange 2003 - 2010 Coexistence

Should port 25 be open between Exchange 2003 (single server) and our 2 Exchange 2010 Hub/CAS servers during coexistence?

Ex2003 is on our 10.x.x.x old network, and Ex2010 servers on 172.x.x.x new network. Both networks have been bridged together, however when I test Mail Flow should port 25 be open bi-directional on the firewall between the two environments?
CTCRMInfrastructure EngineerAsked:
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parv kumarengineerCommented:
Yes , it should be open.
Manikandan NarayanswamySecurity Specialist & IBM Security GuardiumCommented:

Yes port 25 must be opened. However for your ready reference i am pasting the required ports which are need to be opened for Exchange 2003/2007 to coexist with Exchange 2010



808 (TCP)

Mailbox Replication Service uses to communicate

53 (TCP)


135 (TCP)

RPC End Point

389 (TCP)




1024 > (TCP)

if mailbox store is not statically configured then 1024 higher ports need to be open

88 (TCP)


445 (TCP)

Microsoft-DS Service

443 (TCP)

Mailbox Replication Proxy service uses port 443 to communicate with other Exchange 2010 client access server via HTTPS.

For more information on what ports are used by Exchange 2003 & 2013. Refer the below links


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CTCRMInfrastructure EngineerAuthor Commented:
Thanks Guys
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