When the WordPress plugin DAP (Digital Access Pass) sends an email message, this is the message I get in the log:

server postfix/sendmail[3324]: fatal: Recipient addresses must be specified on the command line or via the -t option

Not surprisingly, the email message doesn't arrive.

This worked a week ago. We can find no changes made in that time.

Where should I look for a bad configuration that would cause this?


There's a lot of ways this could be breaking. It's either a server config issue or a bug in the plugin.

To rule out the server, send a message from the command line using the mail command or similar. If that doesn't work, check your configuration.

  • On Ubuntu, Postfix is easier to work with than sendmail and usually works out of the box.
  • If the message sends but you don't receive it, you might be getting blocked by spam filters. To fix this, you need to set up DKIM and SPF authentication, and make sure your server's IP address is not blacklisted. Or, work around all this by configuring the server to relay outgoing messages to an established email sender, such as Mandrill.

It might be the plugin instead of the server. This is more likely if nothing has changed on the server itself lately and if you've updated Wordpress or your plugins. If this is the case, get in touch with the plugin developer. Meanwhile, you may be able to roll back to a working version if you can figure out what exactly was updated that broke things.

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  • Thanks, Jonathon. I'll need to get DKIM and SPF set back up, I'm sure. – Daniel Wilson Aug 14 '16 at 6:00

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