Synchronet v3.19b-Win32 (install) has been released (Jan-2022).

You can donate to the Synchronet project using PayPal.

Relay Incoming SMTP Mail through Vertrauen

Your ISP restricts or blocks inbound connections to TCP port 25 so you are unable to have the Synchronet Mail Server receive email messages from public mail (SMTP) servers (which by standard convention always attempt delivery on TCP port 25).

Have another Mail Server (listening on TCP port 25) receive mail for your host on your behalf and then forward that mail to your Synchronet Mail Server (on TCP port 587), thus providing the service of a Mail Exchange (MX). Vertrauen can provide this Mail Exchange service for your Synchronet BBS (yes, for free).


  1. Insure your Synchronet Mail Server is configured to accept SMTP mail submissions on port 587 (this is a default configuration, so it should already)
  2. Email digital man and ask for mail exchange services while providing the hostname of your BBS
  3. Once you get confirmation from digital man, you need to setup a DNS MX record for your BBS's hostname:
    • If you are not using the dynamic name service, then you'll need to contact your domain name registrar to add the MX record.
    • Otherwise (you are using, add “ -mx” to the end of your DYNDNS timed event command-line in SCFG->External Programs->Timed Events.

How it Works

  1. When someone sends an email message to, their mail client sends the email message to their outgoing mail server (e.g. their ISP or an email service, like gmail or Yahoo!).
  2. Their outgoing mail server then performs a DNS request for the MX record associated with
  3. The MX record for resolves to
  4. Their outgoing mail server connects to (on TCP port 25, the standard SMTP port) to deliver the mail for
  5. Vertrauen's mail server ( looks up the destination email address (i.e. in its alias.cfg file and accepts the mail message, noting the forwarding address (e.g.
  6. At this point, the email sender's mail server assumes the mail message has been delivered to the recipient successfully
  7. A few moments later, the Vertrauen SendMail Thread attempts to deliver the mail message to If the delivery attempt succeeds, the mail message is deleted on Vertrauen. If the delivery attempt fails, multiple retries are attempted over many hours before the mail message is determined undeliverable and a detailed “bounce message” is created for (and attempted to be delivered to) the original mail sender.

This mail exchange service can be terminated for one or all clients for any reason at any time. Most notably, if your BBS receives excessive SPAM through Vertrauen, you will lose access to this service. Your relayed mail messages are not private and there cannot be any expectation of privacy.

See Also