Sample Google Apps Script to send out bulk mails:

// ── CONFIG ────────────────────────────────────────────────────────────────
const SHEET_NAME  = "Contacts";
const DAILY_LIMIT = 500;        // ← Change to 2000 if you have Google Workspace
const FROM_NAME   = "Ravi Rajamani";

// Column indices (1-based, matching your sheet layout)
const COL_EMAIL   = 1;  // Column A: to_email
const COL_SUBJECT = 7;  // Column G: subject
const COL_BODY    = 8;  // Column H: body
const COL_STATUS  = 9;  // Column I: Status

// ── MAIN FUNCTION ─────────────────────────────────────────────────────────
function sendCampaign() {
  const ss    = SpreadsheetApp.getActiveSpreadsheet();
  const sheet = ss.getSheetByName(SHEET_NAME);

  if (!sheet) {
    Logger.log('ERROR: Sheet "' + SHEET_NAME + '" not found. Check the tab name.');
    return;
  }

  const lastRow = sheet.getLastRow();
  if (lastRow < 2) {
    Logger.log("No data rows found.");
    return;
  }

  // ── READ ALL DATA IN ONE CALL (the key fix) ───────────────────────────
  // This fetches the entire sheet as a 2D array in a single API call,
  // instead of making 4 individual calls per row inside the loop.
  const numRows = lastRow - 1; // exclude header row
  const allData = sheet.getRange(2, 1, numRows, COL_STATUS).getValues();
  // allData[i] is a 0-indexed array for row (i+2) of the sheet
  // allData[i][0] = to_email, [6] = subject, [7] = body, [8] = Status

  Logger.log("Data loaded. Total rows: " + numRows);

  // ── COLLECT ROWS TO SEND ──────────────────────────────────────────────
  // Build a list of {sheetRow, email, subject, body} for unsent rows only.
  // This entire pass is pure in-memory — no Sheets API calls.
  const toSend = [];
  for (let i = 0; i < allData.length; i++) {
    const status = String(allData[i][COL_STATUS - 1]).trim();
    if (status === "Sent") continue;                          // already sent
    if (status.startsWith("Error:")) continue;               // skip permanent errors

    const email   = String(allData[i][COL_EMAIL   - 1]).trim();
    const subject = String(allData[i][COL_SUBJECT - 1]).trim();
    const body    = String(allData[i][COL_BODY    - 1]).trim();

    if (!email || !email.includes("@")) continue;            // bad address
    if (!subject || !body) continue;                         // incomplete row

    toSend.push({ sheetRow: i + 2, email, subject, body });  // sheetRow is 1-based
  }

  Logger.log("Unsent rows found: " + toSend.length);

  if (toSend.length === 0) {
    Logger.log("Campaign complete — all rows have been sent.");
    return;
  }

  // ── SEND EMAILS ───────────────────────────────────────────────────────
  // Batch status updates: collect changes, then write them all at once
  // at the end of the run (or every 50 sends as a safety checkpoint).
  let sentThisRun = 0;
  let errorCount  = 0;
  const statusUpdates = []; // {sheetRow, value}

  const limit = Math.min(DAILY_LIMIT, toSend.length);

  for (let j = 0; j < limit; j++) {
    const { sheetRow, email, subject, body } = toSend[j];

    try {
      MailApp.sendEmail({
        to:      email,
        subject: subject,
        body:    body,
        name:    FROM_NAME
      });

      statusUpdates.push({ sheetRow, value: "Sent" });
      sentThisRun++;

      if (sentThisRun % 50 === 0) {
        // Checkpoint write every 50 sends so progress isn't lost if we time out
        flushStatusUpdates(sheet, statusUpdates);
        Logger.log("Checkpoint: " + sentThisRun + " sent so far...");
      }

    } catch (e) {
      statusUpdates.push({ sheetRow, value: "Error: " + e.message });
      errorCount++;
      Logger.log("FAILED row " + sheetRow + " (" + email + "): " + e.message);
    }

    // 200ms pause to stay within Gmail's per-second rate limit
    Utilities.sleep(200);
  }

  // ── FINAL WRITE ───────────────────────────────────────────────────────
  // Write any remaining status updates not yet flushed
  flushStatusUpdates(sheet, statusUpdates);

  // ── SUMMARY ───────────────────────────────────────────────────────────
  Logger.log("─────────────────────────────────────");
  Logger.log("Run complete.");
  Logger.log("Sent this run:   " + sentThisRun);
  Logger.log("Errors this run: " + errorCount);
  Logger.log("Remaining:       " + (toSend.length - sentThisRun));
  Logger.log("─────────────────────────────────────");
}

// ── HELPER: batch-write all pending status updates ─────────────────────────
// Clears the array after writing so we don't double-write on checkpoints.
function flushStatusUpdates(sheet, updates) {
  if (updates.length === 0) return;
  for (const { sheetRow, value } of updates) {
    sheet.getRange(sheetRow, COL_STATUS).setValue(value);
  }
  SpreadsheetApp.flush(); // force Sheets to commit writes immediately
  updates.length = 0;     // clear in-place so the caller's array is emptied
}