BRU-Server is the network backup-solution that I’ve been managing for a lab at UNIL for several years; It backs-up an Xsan filesystem (OS X) involving about 7TB of data sent to a Tandberg robotic tape-library. We occasionally get thrown a curve-ball while keeping it humming….

NOK1: Despite the scheduled backups succeeding, we’ve stopped receiving emails of the backup-successes.  – Outbound emails are being rejected with a “Sending mail to 550 Sender verify failed” error. This changed, at one point, to “550, ‘Verification failed for <[email protected]macsrv1.local> Unrouteable address Sender verify failed’.

SOLUTION: Ensure that your server machine has a FQHN set.
ie. % sudo scutil –set HostName machinename.domain.countrycode

The BRU Server daemon contains a built-in MTA so doesn’t require any email, nor SMTP server running on the BRU Server server system. But it needs to know how to find the destination mail server and also to be able to identify itself using a standard domain name (DNS) via DNS or /etc/hosts. Having a perfectly fine Postfix installation that allows CLI mails to reach their endpoints has little influence on BRU’s MTA success in sending emails out.

Callback verification, aka callout-verification or Sender-Address Verification, is a technique used by SMTP software to validate e-mail addresses. The most common target is the sender address from the message envelope (the address specified during the SMTP dialogue as “MAIL FROM”). [ed: Other techniques involve seeing if the remote server does not respond, or signals that it does not accept bounces, auto-replies, or receipt-confirmations][ed: Callback verification can still work if rejecting all bounces happens at the DATA stage instead of the earlier MAIL FROM stage, while rejecting invalid e-mail addresses remains at the RCPT TO stage instead of also being moved to the DATA stage.] It is mostly used as an anti-spam measure. [wikipedia]

BRU’s MTA looks up the MX records in our domain’s DNS zone, and so contacts OS X defaults to naming a computer using “computername.local” instead of a Fully Qualified Domain Name (FQDN) like “computer name.domain.code.

The following strategies had failed to solve the problem, but may help you.

  • Create a real local user named “bru-server” so that Sender Verify succeeds.
  • Add to /etc/hosts an entry for ‘mail’ specifying our mail server
  • Tell BRU to email [email protected] – NOK: results in ‘Sending mail to localhost Error sending mail: Connection unexpectedly closed’ despite having a working mail server and CLI mail succeeding fine.

Read more in these helpful posts:

  • Sender Verification, 2008 – link
  • BRU Primer, 2008 – link
  • Sender Address Verification: Still a Bad Idea – link
  • Limitations of address verification – link
  • Troubleshooting the MTA – link
  • Enabling postfix (sendmail) on Mac OS X – link
  • My BRU Server system seems to have problems communicating, why? – link

p.s. You might also check that A-Record (in the global internet DNS) points to the same server that the MX-Record points to.  If they differ, you should be aware of it and perhaps need to deal with that.
Also: Our BRU server was 2.0.2 so your results with other versions may differ.