A default program on mac os x that handles mail

The default program on Mac OS X that handles mail is Mail.app, which is a built-in email client that comes pre-installed with macOS. Mail.app allows users to send and receive email, manage their email accounts, and organize their messages using labels and filters.

Mail.app is a simple and easy-to-use email client that supports a variety of email protocols, including POP3, IMAP, and Exchange. It also includes features such as:

• Support for multiple email accounts
• Spam filtering and reporting
• Threaded conversations
• Labels and filters for organizing messages
• Integration with other Apple apps, such as Contacts and Calendar
• Support for attachments and file sharing

However, it's worth noting that Mail.app is not the only email client available for Mac OS X. There are many other third-party email clients available, such as Mozilla Thunderbird, Microsoft Outlook, and Airmail, that offer additional features and customization options.