diff --git a/smmapdfw/doc/smmapdfw.texi b/smmapdfw/doc/smmapdfw.texi
index 1d5bf0e..2a47ff2 100644
--- a/smmapdfw/doc/smmapdfw.texi
+++ b/smmapdfw/doc/smmapdfw.texi
@@ -55,6 +55,26 @@ Plugin
 * Sender-address verifier::     
 * Cyrus mailbox checker::       
 
+API
+
+* Plugin interface::            
+* Obtaining configuration data::  
+* More or less useful stuff::   
+
+Plugin interface
+
+* name::                        
+* Container setup function::    
+* Container destroy function::  
+* Worker setup function::       
+* Worker destroy function::     
+* Worker function::             
+
+Obtaining configuration data
+
+* Without default value::       
+* With default value::          
+
 @end detailmenu
 @end menu
 
@@ -378,5 +398,298 @@ Port to be used for the lmtp dialog.
 @chapter API
 API documentation for plugin programmers
 
+@menu
+* Plugin interface::            
+* Obtaining configuration data::  
+* More or less useful stuff::   
+@end menu
+
+@node Plugin interface, Obtaining configuration data, API, API
+@section Plugin interface
+
+Each plugin has to defined a class descriptor of the type
+@code{class_descriptor_t}.
+
+@verbatim
+struct class_descriptor_s {
+  char *name;
+  int (*init_function)(cfgl_t *cfg, void **handle);
+  int (*destroy_function)(void *handle);
+  int (*work_setup_function)(void *handle, void **work_handle);
+  int (*work_function)(void *handle, void *work_handle, char *input, 
+                       char *output);
+  int (*work_destroy_function)(void *handle, void *work_handle);
+};
+
+typedef struct class_descriptor_s class_descriptor_t;
+
+@end verbatim
+
+The variable name of the class descriptor must be the same as the
+configuration section name from the configuration file. As an example:
+here is the descriptor of the verifier plugin:
+
+@verbatim
+class_descriptor_t verifier = {
+  "verifier",
+  &verify_init,
+  &verify_destroy,
+  &verify_work_setup,
+  &verify_work,
+  &verify_work_destroy
+};
+
+@end verbatim
+
+@menu
+* name::                        
+* Container setup function::    
+* Container destroy function::  
+* Worker setup function::       
+* Worker destroy function::     
+* Worker function::             
+@end menu
+
+@node name, Container setup function, Plugin interface, Plugin interface
+@subsection @code{name}
+
+This is the name of the plugin. It must match to the name of the
+plugin descriptor and the name of the plugin's configuration section.
+
+@node Container setup function, Container destroy function, name, Plugin interface
+@subsection Container setup function: @code{init_function}
+
+@code{int (*init_function)(cfgl_t *cfg, void **handle);}
+
+The Container setup function is called at start up time. A handle to
+access the configuration is handed over and the container handle is
+expected back.
+
+Each plugin defines its own structure for the container
+handle. Certainly it will store the configuration handle within.
+
+
+@node Container destroy function, Worker setup function, Container setup function, Plugin interface
+@subsection Container destroy function: @code{destroy_function}
+
+@code{int (*destroy_function)(void *handle);}
+
+The Container destroy function is called when the plugin is
+unloaded. Is happens currently never.
+
+However, free any resources allocated for the container within this
+function.
+
+
+@node Worker setup function, Worker destroy function, Container destroy function, Plugin interface
+@subsection Worker setup function: @code{work_setup_function}
+
+@code{int (*work_setup_function)(void *handle, void **work_handle);}
+
+The worker setup function is called when the first request of one
+connection is dispatched to the plugin. The container handle is
+provided, the worker handle is expected back.
+
+Each plugin defines its own structure for the worker handle.
+
+
+@node Worker destroy function, Worker function, Worker setup function, Plugin interface
+@subsection Worker destroy function: @code{work_destroy_function}
+
+@code{int (*work_destroy_function)(void *handle, void *work_handle);}
+
+The worker destroy function is called when the connection associated
+with the worker is closed.
+
+Free any resources allocated for this worker. Do not free resources
+associated with the container.
+
+@node Worker function,  , Worker destroy function, Plugin interface
+@subsection Worker function: @code{work_function}
+
+@code{int (*work_function)(void *handle, void *work_handle, char *input, char *output);}
+
+The worker function is called for each request dispatched to this
+plugin. The container handle, the worker handle and of course the
+input is provided.
+
+The return value must be one of
+
+@verbatim
+#define SMM_OK 1
+#define SMM_TEMP_NOK 2
+#define SMM_PERM_NOK 3
+#define SMM_NOT_FOUND_NOK 4
+
+@end verbatim
+
+which matches to the codes sendmail expects in the response from a
+socket map.
+
+@code{output} is the text returned with the code to
+sendmail. Especially for @code{SMM_OK} this is the return value of the
+map.
+
+
+@node Obtaining configuration data, More or less useful stuff, Plugin interface, API
+@section Obtaining configuration data
+
+Each plugin can easily obtain data from its own configuration section.
+
+
+@menu
+* Without default value::       
+* With default value::          
+@end menu
+
+@node Without default value, With default value, Obtaining configuration data, Obtaining configuration data
+@subsection Without default value
+
+@code{char *findcfgl(config_item_t *cfg, char *name);}
+
+@table @samp
+@item cfg
+Configuration handle, handed over to the plugin through the container
+setup function.
+
+@item name
+Name of the configuration parameter.
+@end table
+
+The value of the request configuration parameter is returned. If it
+does not exist, @code{NULL} is returned.
+
+@node  With default value,  , Without default value, Obtaining configuration data
+@subsection With default value
+
+@code{char *findcfglx(config_item_t *cfg, char *name, char *default_value);}
+
+@table @samp
+@item cfg
+Configuration handle, handed over to the plugin through the container
+setup function.
+
+@item name
+Name of the configuration parameter.
+
+@item default_value
+Default value to be returned instead of @code{NULL} if the parameter
+is not mentioned in the configuration file.
+@end table
+
+
+
+@node More or less useful stuff,  , Obtaining configuration data, API
+@section More or less useful stuff
+
+The functions of the library are discussed here for each of the header files.
+
+@node
+@subsection @code{count.h}
+
+This is a threadsafe counter, wrapped around an @code{int}.
+
+Define or allocate a handle of type @code{count_t} to use it.
+
+It defines the following functions of hopefully obvious meaning:
+
+@verbatim
+void count_init(count_t *c);
+void count_destroy(count_t *c);
+int count_inc(count_t *c);
+int count_dec(count_t *c);
+int count_get(count_t *c);
+@end verbatim
+
+
+@node
+@subsection @code{queue.h}
+
+This is a threadsafe queue. Pointers to anything (@code{void}) can be
+stored in it.
+
+Define or allocate a handle of type @code{ht_queue_t} to use it.
+
+It defines the following functions of hopefully obvious meaning:
+
+@verbatim
+void queue_init(ht_queue_t *q);
+void queue_destroy(ht_queue_t *q);
+int queue_put(ht_queue_t *q, void *d);
+void *queue_get_wait(ht_queue_t *q);
+@end verbatim
+
+
+@node
+@subsection @code{htdns.h}
+
+This is a wrapper around the resolver library selected at build time
+(currently traditional @code{libresolv} or djbdns).
+
+It defines the following functions:
+
+@verbatim
+void free_rrs(void **resp);
+mx_rdata_t** get_mx_rrs(char *domain);
+mx_rdata_t** get_best_mx_rrs(char *domain);
+a_rdata_t** get_a_rrs(char *domain);
+cname_rdata_t** get_cname_rrs(char *domain);
+@end verbatim
+
+For details on the data types look into the header file.
+
+Don't forget to free anything you got using @code{free_rrs}.
+
+@node
+@subsection @code{htmalloc.h}
+
+This provides variants of @code{malloc}, @code{realloc} and
+@code{strdup} which either returns or in case of out-of-memory sends
+the whole process into nirwana.
+
+@verbatim
+void *htmalloc(size_t size);
+void *htrealloc(void *ptr, size_t size);
+char *htstrdup(const char *s);
+@end verbatim
+
+
+@node
+@subsection @code{smtp.h}
+
+This is a simple smtp library, also useable for lmtp.
+
+Define or allocate a handle of type @code{smtp_t} to use it.
+
+@verbatim
+smtp_t *smtp_init2(char *host_address, int port, int timeout);
+smtp_t *smtp_init(unsigned int address, int port, int timeout);
+void smtp_destroy(smtp_t *handle);
+
+int smtp_response(smtp_t *handle, char **response);
+int smtp_command(smtp_t *handle, char *command, char *arg);
+
+int smtp_connect(smtp_t *handle);
+int smtp_close(smtp_t *handle);
+
+int smtp_helo(smtp_t *handle, char *arg);
+int smtp_ehlo(smtp_t *handle, char *arg);
+int smtp_lhlo(smtp_t *handle, char *arg);
+int smtp_mailfrom(smtp_t *handle, char *arg);
+int smtp_rcptto(smtp_t *handle, char *arg);
+int smtp_data(smtp_t *handle);
+int smtp_datasend(smtp_t *handle, char *data);
+int smtp_dataend(smtp_t *handle);
+int smtp_rset(smtp_t *handle);
+int smtp_quit(smtp_t *handle);
+@end verbatim
+
+Note: @code{host_address} in @code{smtp_init2} is a quad-dotted IP
+address, no hostname.
+
+@node
+@subsection @code{safe_write.h}
+
+
 
 @bye