Sending e-mail to multiple recipients via SMTP in WordPress

First published on July 24, 2009

By default, e-mails sent from within a WordPress installation use the wp_mail() function (find it in wp-includes/pluggable.php), which in turn uses PHP’s mail() function. Therefore, e-mail is sent using whatever is configured for your server.

You can specify to WordPress that you want to use a particular SMTP server to send e-mail. Plugins such as the aptly named WP Mail SMTP enable you to specify this, including a username and password if required.

However, up to and including WordPress 2.9, if you send mail via SMTP, it does not allow you to e-mail multiple recipients in the “to” field. Most users don’t ever have to deal with this limitation, but if you’re using WordPress in one of several ways (such as with a collaboration workflow), this can cause frustration.

Luckily, the wp_mail() function can be overridden. Specifically, you want to replace this code:

// Set destination address
$phpmailer->AddAddress( $to );

With this:

// Set destination address(es)
// Accept either a comma-separated list or an array
$to = explode( ',', implode( ',', (array) $to ) );
foreach ( $to as $to_recipient ) {
    $phpmailer->AddAddress( trim( $to_recipient ) );

The best practice in such a case is to use a plugin so that whenever you upgrade WordPress, you won’t lose changes. Here is an example of such a plugin, which copies the default wp_mail() function and makes the change as detailed above. To install it, just rename the extension to “php”, put it in your WordPress plugins folder, and activate it.


4 Responses to “Sending e-mail to multiple recipients via SMTP in WordPress”

  1. Roger says:

    Thanks Peter. As a new but rather techy WordPress user, I am both delighted and overwhelmed by its myriad features and intricacies. So such little gems are always useful to collect :-)


  2. Eddie says:

    Thanks, that worked great! It is hard to believe that we would have to wait for WP 3.0 to get this fixed.

    Question: is there a way to modify the code and send mail one recipient at a time, one recipient per TO: ?

    Reply from Peter: Yes, you could modify the wp_mail code further, but a cleaner and more maintainable way is for you to change the code that calls the wp_mail function — on a general basis, this means looping through the addresses you have and calling the function once per address. (For my use, I wanted all “to” addresses to be displayed so that everybody knew who else was being e-mailed.)

  3. Stacey says:

    Is there a way to included the post content in the email? We want people to be able to review the post via their mobile email.

    Reply from Peter: I’m assuming that you’re referring to the collaboration e-mails plugin? You could certainly edit the pce_pending() function in the plugin file and output different aspects of the post as available in the $pce_object variable.

  4. Dan Stramer says:

    Thanks alot peter, that fixed my problem.
    By the way – the plugin link does not work


    Reply from Peter: Thanks for pointing that out. I’ve fixed the link now.

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