I recently switched to the latest version of SmarterMail 8629 (Aug 17, 2023) from version 14. The update worked without problems and has been working fine for a couple of weeks until yesterday when several customers called me to report that their email was returned because it was not being signed (DKIM).
Remote server returned '550 5.7.509 Access denied, sending domain XXXXXX.COM does not pass DMARC verification and has a DMARC policy of reject.'
I checked the logs and for no apparent reason some domains stopped signing mail (DKIM). The delivery log showed in all shipments from those domains:
[2023.09.11] 20:11:15.180  Exception getting DKIM signature System.NullReferenceException: Object reference not set to an instance of an object.
[2023.09.11] at SmarterMail.Common.MailSigning.DKIM.DKIM.Sign(MimeMessage mime, db_domain_settings_readonly domainSettings, DkimSignatureField sigField, MessageSigningArgs signingArgs, List`1& logLines) at MailService.RelayServer.RemoteDeliverySession.GetDkimS signature()
The configuration in Smartermail was correct. The DNS records had not been changed. Even from the server with nslookup I could see the correct selector key and mxtoolbox was not reporting any problems. Turning DKIM on and off did not solve the problem.
The only entry I found on this problem was:
But in my case, the configuration was correct.
Restarting the server did not fix the problems. Finally I decided to change the keys by regenerating in SmarterMail, update DNS, and the signing started working without problems.
Without changing anything on the server, without changing anything in DNS, without rebooting, it's very strange.
Has anyone had these problems?