Duplicate reminders sent out last night

These kinds of things will be very tough to track down the cause, especially if it was working fine and then for some unknown reason starting acting like this. So far, I have not had any other reports of anything similar, and unless I can somehow reproduce the issue, it will be very hard to figure out what is happening. As far as I can recall, I have made no changes to my email functions recently, other than adding an additional email template tag so more info could be added to the email message.

Are you using the feature to limit the number of emails sent out each hour? Are you using the default WordPress/server email functions? Or have you installed something better like an SMTP mailer plugin? Have you checked your server logs and email logs to try to see if there were any errors reported during the time the emails were being sent?

Thank you. I am using the Postman plugin which sends mails through the GMail API. I have noticed that e-mails from another plugin are also sent out irregularly and/or several times. Some Postman testmails are send out, but also generate an error. Possibly this casuses some kind of retry in plugins that try to mail. Does your plugin contain something like a retry mechanism?

I will investigate this further.

That sounds like the issue… something is causing some kind of error during the sending of the email (although the email is actually getting sent), and so the wp_mail function is returning a false value. Note that plugins, like Postman, are simply replacing the pluggable wp_mail function to send emails via SMTP instead of PHP sendmail, so my own plugin is not aware of how the email is actually being sent. My plugin just formats the email data and then calls the wp_mail function to actually send the email. My plugin does NOT have a retry function, so it will not try to send an email again immediately when a FALSE value is returned from wp_mail (so most notifications, such as sign-ups and clear emails will NOT be sent multiple times). However, if a true/positive value is NOT returned from wp_mail when it is sending reminders, then those reminders never get marked as being sent and will be resent again the next time the CRON job runs.

Not much I could do about that in my plugin unless I change my code to always mark reminders as being sent, even when wp_mail returns a false value. But, that would be like treating the symptom of a problem instead of fixing the problem.

So, for now, I’ll mark this as resolved since my plugin is working as designed, and you should contact the developer for Postman (which I also use, btw) to see if they can help you track down the issue with your email/server configuration.

Thanks for your assistance. I now can confirm that the issue was caused by the Postman plugin. Today I found the cause and a solution / workaround.

Some time ago I increased the size of the log from 250 to 1.000. Today I discovered that there where almost 7.000 log lines in de posts table. I then completely turned of logging and the Ajax error did not occur anymore.

After that, I used a Delete plugin to delete the 7.000 obsolete posts 500 at a time. That took some time. I assume the error was caused by the log delete routine that simply took too long…

Since I don’t need logging anymore, I won’t turn it on again. My problem is solved now.