Effects of Blocking Port 25

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  • Hosts not on the designated servers list will not be able to send email. Subscribers must provide MOREnet with an accurate and complete list of email servers (and other hosts that are permitted to send email using their own SMTP engines, such as student records systems and other administrative systems).
Failure to provide an accurate and complete list of email servers will result in servers not on the list being unable to send email. Although most systems will queue mail and attempt to deliver it later, some messages could be lost. It is imperative that customers using GNN Phase 2 examine all SMTP traffic originating from their networks to ensure that important servers don't get inadvertently blocked. MOREnet Security can assist with this analysis.
  • Some users may not be able to send email using certain stand alone email clients. Most legitimate email servers require users either to be on the same network subnet as the mail server or to authenticate to the mail server prior to relaying mail. If a server does not have these requirements, GNN Phase 2 might prevent a user from sending email from servers located outside the customer network.
  • Authenticated email may be sent on ports other than port 25 and will not be affected by this service. Users of the kinetic service access email this way and will not be affected. For example, some services require users to establish an authenticated SSL session over port 465 or port 587. None of these services will experience issues after the implementation of GNN Phase 2.

Sites using web-based email will be unaffected by GNN Phase 2.