diff --git a/src/transport.c b/src/transport.c
index 160feeae..573c990c 100644
--- a/src/transport.c
+++ b/src/transport.c
@@ -1,6 +1,5 @@
 #include "pEp_internal.h"
 
-#include <stdlib.h>
 #include <memory.h>
 #include <assert.h>
 
@@ -21,3 +20,175 @@ void release_transport_system(PEP_SESSION session)
 {
     // nothing yet
 }
+
+pEp_identity *identity_dup(const pEp_identity *src)
+{
+    pEp_identity *dup = new_identity(src->address, src->fpr, src->user_id, src->username);
+    assert(dup);
+    if (dup == NULL)
+        return NULL;
+    
+    dup->address_size = strlen(dup->address);
+    dup->fpr_size = strlen(dup->fpr);
+    dup->user_id_size = strlen(dup->user_id);
+    dup->username_size = strlen(dup->username);
+    dup->comm_type = src->comm_type;
+    dup->lang[0] = src->lang[0];
+    dup->lang[1] = src->lang[1];
+    dup->lang[2] = 0;
+    dup->me = src->me;
+}
+
+identity_list *new_identity_list(const pEp_identity *ident)
+{
+    identity_list *id_list = calloc(1, sizeof(identity_list));
+    assert(id_list);
+    if (id_list == NULL)
+        return NULL;
+
+    if (ident) {
+        id_list->ident = identity_dup(ident);
+        assert(id_list->ident);
+        if (id_list->ident == NULL) {
+            free(id_list);
+            return NULL;
+        }
+    }
+
+    return id_list;
+}
+
+void free_identity_list(identity_list *id_list)
+{
+    if (id_list) {
+        free_identity_list(id_list->next);
+        free_identity(id_list->ident);
+        free(id_list);
+    }
+}
+
+identity_list *identity_list_add(identity_list *id_list, const pEp_identity *ident)
+{
+    assert(id_list);
+    assert(ident);
+
+    if (id_list->ident == NULL) {
+        id_list->ident = identity_dup(ident);
+        assert(id_list->ident);
+        if (id_list->ident == NULL)
+            return NULL;
+        else
+            return id_list;
+    }
+    else if (id_list->next == NULL) {
+        id_list->next = new_identity_list(ident);
+        assert(id_list->next);
+        return id_list->next;
+    }
+    else {
+        return identity_list_add(id_list->next, ident);
+    }
+}
+
+message *new_message(
+        msg_direction dir,
+        const pEp_identity *from,
+        const pEp_identity *to,
+        const char *shortmsg
+    )
+{
+    message *msg = calloc(1, sizeof(message));
+    assert(msg);
+    if (msg == NULL)
+        return NULL;
+
+    msg->shortmsg = strdup(shortmsg);
+    assert(msg->shortmsg);
+    if (msg->shortmsg == NULL) {
+        free(msg);
+        return NULL;
+    }
+    msg->shortmsg_size = strlen(msg->shortmsg);
+
+    msg->dir = dir;
+
+    msg->from = identity_dup(from);
+    assert(msg->from);
+    if (msg->from == NULL) {
+        free_message(msg);
+        return NULL;
+    }
+
+    if (dir == dir_incoming) {
+        msg->recv_by = identity_dup(to);
+        assert(msg->recv_by);
+        if (msg->recv_by == NULL) {
+            free_message(msg);
+            return NULL;
+        }
+    }
+
+    msg->to = new_identity_list(to);
+    assert(msg->to);
+    if (msg->to == NULL) {
+        free_message(msg);
+        return NULL;
+    }
+
+    return msg;
+}
+
+void free_message(message *msg)
+{
+    free(msg->id);
+    free(msg->shortmsg);
+    free(msg->longmsg);
+    free(msg->longmsg_formatted);
+    free(msg->rawmsg);
+    free_identity_list(msg->to);
+    free_identity_list(msg->cc);
+    free_identity_list(msg->bcc);
+    free(msg->refering_id);
+    free_message_ref_list(msg->refered_by);
+    free(msg);
+}
+
+message_ref_list *new_message_ref_list(message *msg)
+{
+    message_ref_list *msg_list = calloc(1, sizeof(message_ref_list));
+    assert(msg_list);
+    if (msg_list == NULL)
+        return NULL;
+
+    msg_list->msg_ref = msg;
+
+    return msg_list;
+}
+
+void free_message_ref_list(message_ref_list *msg_list)
+{
+    if (msg_list) {
+        free_message_ref_list(msg_list->next);
+        free(msg_list);
+    }
+}
+
+message_ref_list *message_ref_list_add(message_ref_list *msg_list, message *msg)
+{
+    assert(msg_list);
+    assert(msg);
+
+    if (msg_list->msg_ref == NULL) {
+        msg_list->msg_ref = msg;
+        return msg_list;
+    }
+    else if (msg_list->next == NULL) {
+        msg_list->next = new_message_ref_list(msg);
+        assert(msg_list->next);
+        return msg_list->next;
+    }
+    else {
+        return message_ref_list_add(msg_list->next, msg);
+    }
+}
+
diff --git a/src/transport.h b/src/transport.h
index bcc2b5b3..173ab25d 100644
--- a/src/transport.h
+++ b/src/transport.h
@@ -1,6 +1,10 @@
 #pragma once
 
 #include "pEpEngine.h"
+#include <time.h>
+#include <stdlib.h>
+
+typedef struct tm timestamp;
 
 typedef enum _PEP_transports {
     PEP_trans_auto = 0,
@@ -12,8 +16,75 @@ typedef enum _PEP_transports {
 
 typedef struct _PEP_transport_t PEP_transport_t;
 
-typedef PEP_STATUS (*sendto_t)(PEP_SESSION session, const pEp_identity *address, const char *shortmsg, const char *longmsg, const char *longmsg_formatted);
-typedef PEP_STATUS (*readnext_t)(PEP_SESSION session, pEp_identity *from, pEp_identity *reached, char **shortmsg, size_t shortmsg_size, char ** longmsg, size_t longmsg_size, char ** longmsg_formatted, size_t longmsg_formatted_size, PEP_transport_t **via);
+pEp_identity *identity_dup(const pEp_identity *src);
+
+typedef struct _identity_list {
+    pEp_identity *ident;
+    struct _identity_list *next;
+} identity_list;
+
+identity_list *new_identity_list(const pEp_identity *ident);
+void free_identity_list(identity_list *id_list);
+identity_list *identity_list_add(identity_list *id_list, const pEp_identity *ident);
+
+typedef enum _msg_format {
+    format_plain = 0,
+    format_html
+} msg_format;
+
+typedef enum _msg_direction {
+    dir_incoming = 0,
+    dir_outgoing
+} msg_direction;
+
+struct _message_ref_list;
+
+typedef struct _message {
+    msg_direction dir;
+    char * id;
+    size_t id_size;
+    char * shortmsg;
+    size_t shortmsg_size;
+    char * longmsg;
+    size_t longmsg_size;
+    char * longmsg_formatted;
+    size_t longmsg_formatted_size;
+    msg_format format;
+    char * rawmsg;
+    size_t rawmsg_size;
+    timestamp sent;
+    timestamp recv;
+    pEp_identity *from;
+    identity_list *to;
+    pEp_identity *recv_by;
+    identity_list *cc;
+    identity_list *bcc;
+    char * refering_id;
+    size_t refering_id_size;
+    struct _message *refering_msg;
+    struct _message_ref_list *refered_by;
+} message;
+
+typedef struct _message_ref_list {
+    message *msg_ref;
+    struct _message_ref_list *next;
+} message_ref_list;
+
+message *new_message(
+        msg_direction dir,
+        const pEp_identity *from,
+        const pEp_identity *to,
+        const char *shortmsg
+    );
+
+void free_message(message *msg);
+
+message_ref_list *new_message_ref_list(message *msg);
+void free_message_ref_list(message_ref_list *msg_list);
+message_ref_list *message_ref_list_add(message_ref_list *msg_list, message *msg);
+
+typedef PEP_STATUS (*sendto_t)(PEP_SESSION session, const message *msg);
+typedef PEP_STATUS (*readnext_t)(PEP_SESSION session, message **msg, PEP_transport_t **via);
 
 struct _PEP_transport_t {
     uint8_t id;