Hello! 
I'm currently facing some challenges with my LilyGO T-SIM7000G module, and I'm hoping to get some assistance.
My ultimate objective is to utilize this module to send emails via LTE. In the future, I plan to have the module collect data from a sensor and send these data as CSV files via email. However, at the moment, I'm encountering difficulties with even sending a basic email. It seems there is a problem with the network connection because its not possible to log in. On the other hand it says that it is connected...
I would greatly appreciate any guidance or insights you can offer in order to make progress with my LilyGO T-SIM7000G module.
Thank you in advance for your help! 
/* Sketch ist eine Mischung aus dem Sketch für die Testung der SIM7000G https://github.com/Xinyuan-LilyGO/LilyGO-T-SIM7000G/blob/master/examples/Arduino_TinyGSM/AllFunctions/AllFunctions.ino
und dem GSM Code Example der ESP_Mail_Client Libary https://github.com/mobizt/ESP-Mail-Client/commit/c6ce44ffcd86a94b812cea049716b109f8c0dbc0#diff-2fe767a3f54685ccde84ec2c14d6f12f6fb0cb93a03e8953dbfeb5d01f2dc72e */
#define TINY_GSM_MODEM_SIM7000
#include <TinyGsmClient.h>
#define TINY_GSM_RX_BUFFER 1024 // Set RX buffer to 1Kb
#define SerialAT Serial1
#define TINY_GSM_TEST_GPRS true
#define TINY_GSM_USE_WIFI false
#define TINY_GSM_POWERDOWN true
// Setze GSM-PIN, falls vorhanden -->muss auch definert werden wenn kein PIN nötig ist
#define GSM_PIN ""
// Deine GPRS-Zugangsdaten der SIM Karte
const char apn[] = "iot.1nce.net"; // APN
const char gprsUser[] = "";
const char gprsPass[] = "";
#include <ESP_Mail_Client.h>
#include <SPI.h>
#include <SD.h>
#include <Ticker.h>
#define uS_TO_S_FACTOR 1000000ULL // Conversion factor for micro seconds to seconds
#define TIME_TO_SLEEP 60 // Time ESP32 will go to sleep (in seconds)
//Pinout für SIM Karte
#define UART_BAUD 115200
#define PIN_DTR 25
#define PIN_TX 27
#define PIN_RX 26
#define PWR_PIN 4
//Pinout für SD Karte
#define SD_MISO 2
#define SD_MOSI 15
#define SD_SCLK 14
#define SD_CS 13
#define LED_PIN 12
int counter, lastIndex, numberOfPieces = 24;
String pieces[24], input;
TinyGsm modem(SerialAT);
TinyGsmClient gsm_client(modem); // basic non-secure client
/* The smtp host name e.g. smtp.gmail.com for GMail or smtp.office365.com for Outlook or smtp.mail.yahoo.com*/
#define SMTP_HOST "****"
#define SMTP_PORT 465
/* The sign in credentials*/
#define AUTHOR_EMAIL "*******"
#define AUTHOR_PASSWORD "*****"
/* Recipient's email*/
#define RECIPIENT_EMAIL "*******"
SMTPSession smtp; //Erstellung Klasse und Objekt
// Callback-Funktion, um den Status des E-Mail-Versands zu überprüfen
void smtpCallback(SMTP_Status status);
// Wartezeit vor der Anmeldung am E-Mail-Server (in Millisekunden)
const unsigned long emailLoginDelay = 20000; // Zum Beispiel 10 Sekunden
void setup()
{
// Baudrate
Serial.begin(115200);
delay(10);
// Set LED OFF
pinMode(LED_PIN, OUTPUT);
digitalWrite(LED_PIN, HIGH);
pinMode(PWR_PIN, OUTPUT);
digitalWrite(PWR_PIN, HIGH);
// Starting the machine requires at least 1 second of low level, and with a level conversion, the levels are opposite
delay(1000);
digitalWrite(PWR_PIN, LOW);
Serial.println("\nWait...");
delay(1000);
SerialAT.begin(UART_BAUD, SERIAL_8N1, PIN_RX, PIN_TX);
// Restart takes quite some time
// To skip it, call init() instead of restart()
Serial.println("Initializing modem...");
if (!modem.restart()) {
Serial.println("Failed to restart modem, attempting to continue without restarting");
}
}
void loop()
{
// Restart takes quite some time
// To skip it, call init() instead of restart()
Serial.println("Initializing modem...");
if (!modem.init()) {
Serial.println("Failed to restart modem, attempting to continue without restarting");
}
String name = modem.getModemName();
delay(500);
Serial.println("Modem Name: " + name);
String modemInfo = modem.getModemInfo();
delay(500);
Serial.println("Modem Info: " + modemInfo);
#if TINY_GSM_TEST_GPRS
// Unlock your SIM card with a PIN if needed
if ( GSM_PIN && modem.getSimStatus() != 3 ) {
modem.simUnlock(GSM_PIN);
}
#endif
modem.sendAT("+CFUN=0");
if (modem.waitResponse(10000L) != 1) {
DBG(" +CFUN=0 false ");
}
delay(200);
/*
2 Automatic
13 GSM only
38 LTE only
51 GSM and LTE only
* * * */
bool res = modem.setNetworkMode(2);
if (!res) {
DBG("setNetworkMode false ");
return ;
}
delay(200);
/*
1 CAT-M
2 NB-Iot
3 CAT-M and NB-IoT
* * */
res = modem.setPreferredMode(3);
if (!res) {
DBG("setPreferredMode false ");
return ;
}
delay(200);
modem.sendAT("+CFUN=1");
if (modem.waitResponse(10000L) != 1) {
DBG(" +CFUN=1 false ");
}
delay(200);
#if TINY_GSM_TEST_GPRS
SerialAT.println("AT+CGDCONT?");
delay(500);
if (SerialAT.available()) {
input = SerialAT.readString();
for (int i = 0; i < input.length(); i++) {
if (input.substring(i, i + 1) == "\n") {
pieces[counter] = input.substring(lastIndex, i);
lastIndex = i + 1;
counter++;
}
if (i == input.length() - 1) {
pieces[counter] = input.substring(lastIndex, i);
}
}
// Reset for reuse
input = "";
counter = 0;
lastIndex = 0;
for ( int y = 0; y < numberOfPieces; y++) {
for ( int x = 0; x < pieces[y].length(); x++) {
char c = pieces[y][x]; //gets one byte from buffer
if (c == ',') {
if (input.indexOf(": ") >= 0) {
String data = input.substring((input.indexOf(": ") + 1));
if ( data.toInt() > 0 && data.toInt() < 25) {
modem.sendAT("+CGDCONT=" + String(data.toInt()) + ",\"IP\",\"" + String(apn) + "\",\"0.0.0.0\",0,0,0,0");
}
input = "";
break;
}
// Reset for reuse
input = "";
} else {
input += c;
}
}
}
} else {
Serial.println("Failed to get PDP!");
}
Serial.println("\n\n\nWaiting for network...");
if (!modem.waitForNetwork()) {
delay(10000);
return;
}
if (modem.isNetworkConnected()) {
Serial.println("Network connected");
}
Serial.println("\n---Starting GPRS TEST---\n");
Serial.println("Connecting to: " + String(apn));
if (!modem.gprsConnect(apn, gprsUser, gprsPass)) {
delay(10000);
return;
}
if (modem.isNetworkConnected()) {
Serial.println("Gerät ist mit dem Mobilfunknetzwerk verbunden.");
} else {
Serial.println("Gerät ist NICHT mit dem Mobilfunknetzwerk verbunden.");
// Hier können Sie geeignete Maßnahmen ergreifen, wenn keine Netzwerkverbindung besteht.
}
Serial.print("GPRS status: ");
if (modem.isGprsConnected()) {
Serial.println("connected");
} else {
Serial.println("not connected");
}
String ccid = modem.getSimCCID();
Serial.println("CCID: " + ccid);
String imei = modem.getIMEI();
Serial.println("IMEI: " + imei);
String cop = modem.getOperator();
Serial.println("Operator: " + cop);
IPAddress local = modem.localIP();
Serial.println("Local IP: " + String(local));
int csq = modem.getSignalQuality();
Serial.println("Signal quality: " + String(csq));
SerialAT.println("AT+CPSI?"); //Get connection type and band
delay(500);
if (SerialAT.available()) {
String r = SerialAT.readString();
Serial.println(r);
}
Serial.println("\n---End of GPRS TEST---\n");
#endif
if (modem.isNetworkConnected()) {
Serial.println("Network connected");
}
Session_Config config;
config.server.host_name = SMTP_HOST;
config.server.port = SMTP_PORT;
config.login.email = AUTHOR_EMAIL;
config.login.password = AUTHOR_PASSWORD;
config.login.user_domain = F("127.0.0.1");
// Declare the SMTP_Message class variable to handle to message being transport
SMTP_Message message;
// Set the message headers
message.sender.name = F("ESP Mail");
message.sender.email = AUTHOR_EMAIL;
message.subject = F("Test sending plain text Email using GSM module");
message.addRecipient(F("Someone"), RECIPIENT_EMAIL);
// Set the message content
message.text.content = "This is simple plain text message";
// Set debug option
smtp.debug(1);
// Set the callback function to get the sending results
smtp.callback(smtpCallback);
smtp.setGSMClient(&gsm_client, &modem, GSM_PIN, apn, gprsUser, gprsPass);
// Verzögerung vor der Anmeldung am E-Mail-Server
delay(emailLoginDelay);
// Versuchen Sie, sich am E-Mail-Server anzumelden und E-Mails zu senden
smtp.connect(&config);
// Start sending Email and close the session
if (!MailClient.sendMail(&smtp, &message))
Serial.println("Error sending Email, " + smtp.errorReason());
}
void smtpCallback(SMTP_Status status)
{
Serial.println(status.info());
if (status.success())
{
// See example for how to get the sending result
}
}
This is always the response I get.
16:29:53.960 -> Initializing modem...
16:29:54.480 -> Modem Name: SIMCOM SIM7000G
16:29:54.967 -> Modem Info: SIM7000G R1529
16:30:01.185 ->
16:30:01.185 ->
16:30:01.185 ->
16:30:01.185 -> Waiting for network...
16:30:02.217 -> Network connected
16:30:02.217 ->
16:30:02.217 -> ---Starting GPRS TEST---
16:30:02.217 ->
16:30:02.217 -> Connecting to: iot.1nce.net
16:30:04.295 -> Gerät ist mit dem Mobilfunknetzwerk verbunden.
16:30:04.295 -> GPRS status: connected
16:30:04.295 -> CCID: 89882280666038388991
16:30:04.295 -> IMEI: 869951035874639
16:30:04.295 -> Operator: Telekom.de 1nce.net
16:30:04.295 -> Local IP: 29671690
16:30:04.295 -> Signal quality: 25
16:30:05.807 ->
16:30:05.807 -> +CPSI: GSM,Online,262-01,0x972d,25554,124 EGSM 900,-61,0,46-46
16:30:05.807 ->
16:30:05.807 -> OK
16:30:05.807 ->
16:30:05.807 ->
16:30:05.807 -> ---End of GPRS TEST---
16:30:05.807 ->
16:30:05.808 -> Network connected
16:30:25.821 -> #### Error, connection closed
16:30:25.821 -> ! E: connection closed
16:30:25.821 ->
16:30:25.821 -> #### Error, not yet log in
16:30:25.821 -> ! E: not yet log in
16:30:25.821 -> Error sending Email, not yet log in