| Address Predicate API | Prototype for an Address Test function |
| Body Cache Callback API | Prototype for a mutt_bcache_list() callback function |
| Browser Function API | Prototype for a Browser Function |
| Colour Parsing API | Prototype for a function to parse color config |
| ►Auto-Completion API | Auto-Completion API |
| ►Compression API | The Compression API |
| Config Module API | Prototype for a Config Definition Function |
| ►Config Definition API | Config item definition |
| ►Config Type API | Type definition for a config item |
| Connection Account API | Function to get some login credentials |
| ►Connection API | The Connection API |
| Account Private Data API | Free the private data attached to the Account |
| ►Command API | Observers of NT_COMMAND will be passed a Command |
| ►Function Dispatcher API | Prototype for a Function Dispatcher |
| Mailbox Private Data API | Free the private data attached to the Mailbox |
| ►Mailbox API | The Mailbox API |
| Enter Function API | Prototype for a Enter Function |
| Email Private Data API | Free the private data attached to the Email |
| Mime Encoder API | Prototype for an encoding function |
| Email Sorting API | Prototype for an email comparison function |
| Expando Parse API | Custom function to parse a format string into a Node |
| Expando Render API | Render an Expando |
| ►Expando Get Data API | Define callback functions to get data to be formatted |
| GUI: Dialog Windows | A Dialog is an interactive set of windows allowing the user to perform some task |
| GUI: Message Windows | The Message Window is a one-line interactive window at the bottom of the screen |
| ►Window API | The Window API |
| Mime Handler API | Prototype for a function to handle MIME parts |
| Header Cache Naming API | Prototype for function to compose hcache file names |
| IMAP Authentication API | Authenticate an IMAP connection |
| ►Menu API | The Menu API |
| File Mapping API | Prototype for a text handler function for mutt_file_map_lines() |
| Hash Data Free API | Prototype for Hash Destructor callback function |
| Hash Generator API | Prototype for a Key hashing function |
| Hash Table Compare API | Prototype for a function to compare two Hash keys |
| List Data Free API | Prototype for a function to free List data |
| Logging API | Prototype for a Logging Function |
| Observer API | Prototype for a notification callback function |
| Sorting API | Prototype for generic comparison function, compatible with qsort_r() |
| Signal Handling API | Prototype for a Signal Handler function |
| ►Crypto API | The Crypto API |
| Parse a pattern API | Prototype for a function to parse a pattern |
| POP Authentication API | Authenticate a POP connection |
| POP Response Parser API | Prototype for a function to handle POP server responses |
| SMTP Authentication API | Authenticate an SMTP connection |
| ►Key Value Store API | The Key Value Store API |