XCLIENT SMTP Extension Support

We do not recommend a setup using XCLIENT, as it lacks different classifiers we have available whilst directly communicating with the real sending server. Additionally using such setup lacks protection against various types of attacks. Finally the solution is not designed to scale specifically for using the XCLIENT SMTP extension.

Spam Experts has built-in support for the XCLIENT SMTP extension, allowing an external MTA to relay email to the incoming filtering solution whilst providing the data as if it originated from another mailserver.

This feature allows to use the incoming email filtering without the MX records directly pointing to the Spam Experts systems.


The extension can be enabled via the Software API:

api_set_trusted_xclient_list(ip_list='') -> "".
Permit connections from the specified IPs to use the XCLIENT SMTP extension. The list should be a JSON list of IP addresses. Note that you should only permit IP addresses that are completely under your control, or someone who you completely trust.

After enabling XCLIENT for e.g. source IP, it can be verified to work using a client that has built-in XCLIENT support such as NGINX or SWAKS.

We do not provide support for such third-party clients.


To test XCLIENT:

swaks -f originalfrom@demo-domain.invalid -t originalto@demo-domain.invalid -s spamexpertsserver.demo-domain.invalid --xclient-name pretend.server.invalid --xclient-addr

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