How to Automate Gmail Templated Replies & Follow-ups using the API

1#!/usr/bin/env python3
2"""Gmail Follow-up Sequence Automator."""
3import os
4import csv
5import base64
6import time
7import logging
8from datetime import datetime, timedelta
9from email.mime.text import MIMEText
10from email.mime.multipart import MIMEMultipart
11from email.header import Header
12from googleapiclient.discovery import build
13from google.oauth2.credentials import Credentials
14from google_auth_oauthlib.flow import InstalledAppFlow
15from google.auth.transport.requests import Request
16
17logging.basicConfig(level=logging.INFO, format='%(asctime)s %(message)s')
18log = logging.getLogger(__name__)
19
20SCOPES = ['https://www.googleapis.com/auth/gmail.send', 'https://www.googleapis.com/auth/gmail.readonly']
21DAILY_LIMIT = 450  # Stay safely under the 500/day @gmail.com cap
22
23TEMPLATES = {
24    'initial': 'Hi {name},\n\nI noticed {company} and thought we might be able to help with {pain_point}.\n\nOpen to a quick 15-minute chat?\n\nBest, Me',
25    'followup_3': 'Hi {name},\n\nJust following up on my last note. Still happy to connect if timing works.\n\nBest, Me',
26    'followup_7': 'Hi {name},\n\nLast note from my end — reach out any time if this becomes relevant.\n\nBest, Me'
27}
28
29def get_service():
30    creds = None
31    if os.path.exists('token.json'):
32        creds = Credentials.from_authorized_user_file('token.json', SCOPES)
33    if not creds or not creds.valid:
34        if creds and creds.expired and creds.refresh_token:
35            creds.refresh(Request())
36        else:
37            flow = InstalledAppFlow.from_client_secrets_file('credentials.json', SCOPES)
38            creds = flow.run_local_server(port=0)
39        with open('token.json', 'w') as f: f.write(creds.to_json())
40    return build('gmail', 'v1', credentials=creds)
41
42def encode_message(sender, to, subject, body, reply_to=None, references=None, thread_id=None):
43    msg = MIMEText(body, 'plain', 'utf-8')
44    msg['From'] = sender
45    msg['To'] = to
46    msg['Subject'] = str(Header(subject, 'utf-8'))
47    if reply_to:
48        msg['In-Reply-To'] = reply_to
49        msg['References'] = references or reply_to
50    raw = base64.urlsafe_b64encode(msg.as_bytes()).decode()
51    result = {'raw': raw}
52    if thread_id: result['threadId'] = thread_id
53    return result
54
55def main():
56    service = get_service()
57    sent_today = 0
58
59    with open('leads.csv') as f:
60        for lead in csv.DictReader(f):
61            if sent_today >= DAILY_LIMIT:
62                log.warning('Daily limit reached, stopping')
63                break
64            try:
65                # Send initial email
66                body = TEMPLATES['initial'].format(**lead)
67                msg = encode_message('me@gmail.com', lead['email'],
68                                     f"Quick question for {lead['company']}", body)
69                sent = service.users().messages().send(userId='me', body=msg).execute()
70                thread_id = sent['threadId']
71                sent_today += 1
72                log.info(f'Sent initial to {lead["email"]} (thread: {thread_id})')
73
74                # Create follow-up drafts
75                for days, key in [(3, 'followup_3'), (7, 'followup_7')]:
76                    follow_body = TEMPLATES[key].format(**lead)
77                    follow_msg = encode_message(
78                        'me@gmail.com', lead['email'],
79                        f"Re: Quick question for {lead['company']}",
80                        follow_body, thread_id=thread_id
81                    )
82                    service.users().drafts().create(userId='me', body={'message': follow_msg}).execute()
83                    log.info(f'Draft created for day {days} follow-up to {lead["email"]}')
84
85                time.sleep(1.5)  # ~40 sends/min max for safety
86            except Exception as e:
87                log.error(f'Failed for {lead["email"]}: {e}')
88                continue
89
90if __name__ == '__main__':
91    main()