I had an extended (24 hour outage) on my home broadband, and several inbound emails ended up bouncing. I set up a couple of backup MX servers at an outside provider, and tested by bringing down the SMTP proxy, then sending a couple of test emails to my home address. Waited a few minutes, and brought it back up. The emails bounced back to my sending email address (at work), with a 550 error. Looking at the logs, I can see it is complaining that one of the backup MX servers doesn't have permission to send from that domain. For the moment, I have just disabled the SPF checking in the proxy. Is there a way to exempt the N backup MX servers from this check?
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