Today I had to install mailparse via PEAR. On installing I came across one of the errors: mbstring not found despite of it was right there. One of the simplest option to fix it is given below. Though I am working on MAMP but it will work with anyone since it’s part of PHP Source. Go to your PHP Source Library. In my case it is: [crayon-5f95526f3a51e720870452/] and add following lines in mbfilter.h [crayon-5f95526f3a527123483830/] and then run PEAR command again [crayon-5f95526f3a529896314217/] If all goes well it should give something like: [crayon-5f95526f3a52a548752058/] Manually add entry of the extension in your php.ini file and it should be available for work.