Only one plugin can overwrite the wp_mail() function. Unfortunately Postman and WPMQ will never be compatible.
Perhaps queueing mail will be added to Postman in the future.
Thanks for your reply. This is interesting, because other plugins which also modify wp_mail (WP-Mail-SMTP for example) do not generate this error, any idea why?
Yup. Because WP-Mail-SMTP and the others do not modify wp_mail.
To the best of my knowledge, there are only a handful of SMTP plugins that override the default WordPress wp_mail() function:
- Cimy Swift – by replacing PHPMailer with Swift Mailer
- Postman – by replacing PHPMailer with Zend Mail/the Gmail API
- wpMandrill – by replacing PHPMailer with the Mandrill API
- SendGrid – by replacing PHPMailer with the SendGrid API
The rest simply use WordPress filters to intercept your mail call, and at the last moment change PHPMailer (the same one that ships with WordPress) to use your own settings.
@ssuess, have you thought of using the Mandrill or Sendgrid SMTP servers to deliver your email? Then you won’t even need a queue.
Mandril says:
“If you send more than your quota in an hour, we won’t delete the mail. We’ll just queue it until the next hour and then deliver it. By then your quota will likely have increased as we respond to your increased volume.”
The next version of Postman will have the Mandrill and Sendgrid API’s in addition to the Gmail API.
The version of Postman in the trunk now has support for the Mandrill and SendGrid API keys, if you’d like to try it out.
Postman 1.7 : https://downloads.wordpress.org/plugin/postman-smtp.zip
