SMTP server issues

Last published : Apr 17, 2026
SMTP-related issues can vary depending on whether the SMTP routing is direct to Enterprise Vault.cloud or indirect, through an on-premises SMTP server.
The most likely reasons for issues with direct SMTP routing are as follows:
  • A firewall is blocking outgoing access to the Internet on port 25.
  • DNS lookups on the journal address domain fail.
The most likely reasons for issues with indirect SMTP routing are as follows:
  • A firewall is blocking the connection to the on-premises SMTP server.
  • The on-premises SMTP server TLS configuration does not match the SMTP TLS configuration setting you specified in Lync Connector.
  • The on-premises SMTP server authentication configuration does not match the SMTP authentication configuration details you specified in Lync Connector.
  • The on-premises SMTP server does not allow relaying. Or relaying is restricted by IP address and the computer on which Lync Connector is installed is not on the allow list.
  • The on-premises SMTP server is unable to relay emails to Enterprise Vault.cloud, for example because DNS lookups on the journal address domain are failing.
  • The SMTP server has a messages size limit that is smaller than the configured maximum email size in Lync Connector.
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