What is SMTP Fastpath and what causes messages to fall back to the normal path?

Issue

What is SMTP Fastpath and what causes messages to fall back to the normal path?

Solution

SMTP Fastpath is an alternative MTA technology, recommended for use on Message Servers.

Fastpath causes SMTP to attempt immediate delivery of messages, if possible. Messages are not queued with SMTP Fastpath, this allows for its speed in delivery. The mail logs on the Mirapoint appliance list the messages that have been sent and received, but not queued.

Restrictions

SMTP Fastpath can be enabled unless either of the following is already enabled:

• TLS-only
• Email billing integration

Activating the Feature

To turn on SMTP Fastpath, use the CLI Smtp Set Fastpath on command.

If SMTP Fastpath is enabled, any of the following conditions cause messages to be delivered using the normal delivery path. These features do not disable Fastpath as the listening MTA, but do cause messages to be queued before delivery.

• A masquerade set
• LDAP masquerade sender set
• "received for header" enabled
• Forwards or auto-replies in LDAP set
• The recipient is in a virtual domain
• The recipient has a non-LDAP forward or autoreply
• The recipient is to a catchall address in a delegated domain
• The recipient has a filter
• The message contains 8-bit MIME and the destination system doesn't support 8-bit MIME
• The message has more than 20 recipients or 20 destinations
• The appliance is determined to be overloaded
• The message contains certain DSN verbs in the envelope
• LMR or OMR is enabled
• LDAP mailgroups

To determine if SMTP Fastpath is running in an optimal state, issue the following commands to ensure they all reply as off or disabled:

Conf Enabled Ldapautoreply

Conf Enabled Ldapforward

Smtp Get Rbl

Smtp Get Smtpauth

Smtp Get Omr

Smtp Get Lmr

Smtp Get Masq

Smtp Get Ldapmasqsender

Smtp Get Receivedforhdr

Fastpath requires a license, which is auto-granted on MOS 3.6 and later releases. The License List command should list the SMTP Fastpath license.

To check if SMTP Fastpath is using the normal path for delivery and queuing messages, use the Log Diagwatch Mta.message.queued command to monitor the event.