src/OwpPostmark.inc.php
public function attachment($name, $content, $content_type)
    {
        $this->data['Attachments'][$this->attachment_count]['Name']         = $name;
        $this->data['Attachments'][$this->attachment_count]['ContentType']  = $content_type;

        // Check if our content is already base64 encoded or not
        if(! base64_decode($content, true))
            $this->data['Attachments'][$this->attachment_count]['Content']  = base64_encode($content);
        else
            $this->data['Attachments'][$this->attachment_count]['Content']  = $content;

        // Up our attachment counter
        $this->attachment_count++;

        return $this;
    }
public function attachment($name, $content, $content_type)
    {
        $this->data['Attachments'][$this->attachment_count]['Name']         = $name;
        $this->data['Attachments'][$this->attachment_count]['ContentType']  = $content_type;

        // Check if our content is already base64 encoded or not
        if(! base64_decode($content, true))
            $this->data['Attachments'][$this->attachment_count]['Content']  = base64_encode($content);
        else
            $this->data['Attachments'][$this->attachment_count]['Content']  = $content;

        // Up our attachment counter
        $this->attachment_count++;

        return $this;
    }
Add Attachment Method

@method mixed attachment($name, $content, $content_type) Add Attachment Method
@access public
@param  $name
@param  $content
@param  $content_type
@return $this