在Flask中實現電子郵件發送可以使用Python的smtplib庫。下面是一個簡單的例子：

from flask import Flask, request
import smtplib
from email.mime.text import MIMEText
from email.mime.multipart import MIMEMultipart

app = Flask(__name__)

def send_email(subject, message, to_email):
    from_email = 'your_email@example.com'
    password = 'your_password'

    msg = MIMEMultipart()
    msg['From'] = from_email
    msg['To'] = to_email
    msg['Subject'] = subject

    msg.attach(MIMEText(message, 'plain'))

    server = smtplib.SMTP('smtp.example.com', 587)
    server.starttls()
    server.login(from_email, password)
    text = msg.as_string()
    server.sendmail(from_email, to_email, text)
    server.quit()

@app.route('/send_email', methods=['POST'])
def send_email_route():
    data = request.get_json()
    subject = data['subject']
    message = data['message']
    to_email = data['to_email']

    send_email(subject, message, to_email)

    return 'Email sent successfully!'

if __name__ == '__main__':
    app.run()

在上面的例子中，我們定義了一個send_email函數來發送電子郵件。然后我們在Flask應用中創建了一個路由/send_email，通過POST請求發送郵件的主題、內容和收件人郵箱地址。當接收到請求時，我們調用send_email函數發送電子郵件。