Here's an example code for installing Mail and Mail_mime in MAMP
update /Applications/MAMP/conf/php5.3/php.ini
line 405 to read:
include_path = ".:/Applications/MAMP/bin/php5/lib/php:/Applications/MAMP/bin/php5.3/lib/php"
Then execute the following commands
/Applications/MAMP/bin/php5.3/bin/pear uninstall Mail /Applications/MAMP/bin/php5.3/bin/pear uninstall Mail_mine /Applications/MAMP/bin/php5.3/bin/pear install -a Mail /Applications/MAMP/bin/php5.3/bin/pear install -a Mail_mine
Now, restart the MAMP servers and you're in!