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!