Here's a code snippet in Python that sends a reminder email:

```
import smtplib
from email.mime.text import MIMEText
from email.mime.multipart import MIMEMultipart
from datetime import date

# set up SMTP server and login credentials
SMTP_SERVER = 'smtp.gmail.com'
SMTP_PORT = 587
SMTP_USERNAME = 'youremail@gmail.com'
SMTP_PASSWORD = 'your_password_here'

# set up email message
msg = MIMEMultipart()
msg['From'] = 'youremail@gmail.com'
msg['To'] = 'recipientemail@gmail.com'
msg['Subject'] = 'Greeting Message Reminder'

# calculate days remaining until target date
target_date = date(2022, 8, 15)
days_remaining = (target_date - date.today()).days

# compose email message body
body = f"Hello,\n\nThis is a reminder that the target date for the greeting message is in {days_remaining} days.\nPlease make sure to prepare and send the message on time.\n\nThank you,\nYour Name Here"

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

# establish SMTP connection and send email
server = smtplib.SMTP(SMTP_SERVER, SMTP_PORT)
server.ehlo()
server.starttls()
server.ehlo()
server.login(SMTP_USERNAME, SMTP_PASSWORD)
text = msg.as_string()
server.sendmail(SMTP_USERNAME, 'recipientemail@gmail.com', text)
server.quit()

print('Reminder email sent successfully!')
```

Make sure to replace the email addresses and login credentials with the appropriate values for your account. Also, adjust the body of the email message as needed to fit your requirements.
Data prevista: 15 agosto 2022 Oggetto: messaggio di saluto
Scrivi un codice che invii un'e-mail di sollecito