Equal signs replace characters in HTML emails sent to subscribers about new posts

[junipersystems]

OS: Windows Server 2008 R2
Mail Server: MS Exchange Server

Problem not in previous versions. Problem traced to wp-includes\class-phpmailer.php lines 2563 - 2578.

Fixed by making following changes (reverted to previous version):

// Begin changes made 2015-09-10 - commented out line 2564, added line 2565 ---------------------------------------------------------------------
//           return $this->fixEOL(quoted_printable_encode($string));
            return quoted_printable_encode($string);
// End of changes -----------------------------------------------------------------------------------------------------------------------------------------------
        }
        // Fall back to a pure PHP implementation
        $string = str_replace(
            array('%20', '%0D%0A.', '%0D%0A', '%'),
            array(' ', "\r\n=2E", "\r\n", '='),
            rawurlencode($string)
        );
        $string = preg_replace('/[^\r\n]{' . ($line_max - 3) . '}[^=\r\n]{2}/', "$0=\r\n", $string);
// Begin changes made 2015-09-10 - commented out line 2576, added line 2577 ---------------------------------------------------------------------
//        return $this->fixEOL($string);
        return $string;
// End of changes -----------------------------------------------------------------------------------------------------------------------------------------------

[johnbillion]

Thank you for the report, junipersystems.

This change was made in [33124]. Needs testing.

[junipersystems]

After further testing I realized that the second change (lines 2576 and 77) was unnecessary.

[cbutlerjr]

The necessary change was made in [36083]

[sevensoutbill]

We found this issue when some notification emails from the Gravity Forms plugin started showing equal signs throughout. With further testing we narrowed the issue down. It seems when forms with paragraph fields that contained large amounts of text were submitted, the equal signs would appear. We're running WordPress 4.5.3 with class-phpmailer.php 5.2.14. After replacing this with 5.2.10 the issue was resolved. Hope this helps!