ZF-11250: mb_send_mail(): Unsupported transfer encoding "quoted-printable" - will be regarded as 8bit
I the the message mentioned above when I am using Zend_Mail on some of our servers.
There is a similar bug report on PEAR about the package Mail_Mime: http://pear.php.net/bugs/bug.php?id=10146
I guess it will need a similar solution as the one mentioned in this bug report.
More information about my system. It is a CentOS 5.5 server with PHP version 5.2.17 from the testing repository of CentOS. The file /etc/php.ini is the standard file delivered by the OS (with "mbstring.func_overload = 7" set).