How to send message to multiple recipients?

Question

I'm having some trouble sending a message to multiple addresses using the Gmail API. I've successfully sent a message to only one address, but get the following error when I include multiple comma-separated addresses in the 'To' field:

An error occurred: https://www.googleapis.com/gmail/v1/users/me/messages/send?alt=json returned "Invalid to header">

I'm using the CreateMessage and SendMessage methods from this Gmail API guide: https://developers.google.com/gmail/api/guides/sending

That guide states that the Gmail API requires messages that are RFC-2822 compliant. I again didn't have much luck using some of these addressing examples in the RFC-2822 guide: https://tools.ietf.org/html/rfc2822#appendix-A

I'm under the impression that '[e-mail], [e-mail], [e-mail]' should be a valid string to pass into the 'to' parameter of CreateMessage, but the error that I received from SendMessage leads me to believe otherwise.

Please let me know if you can recreate this problem, or if you have any advice on where I may be making a mistake. Thank you!

Edit: Here is the actual code that yields an error...

def CreateMessage(sender, to, subject, message_text):
    message = MIMEText(message_text)
    message['to'] = to
    message['from'] = sender
    message['subject'] = subject
    return {'raw': base64.urlsafe_b64encode(message.as_string())}

def SendMessage(service, user_id, message):
    try:
        message = (service.users().messages().send(userId=user_id, body=message)
           .execute())
        print 'Message Id: %s' % message['id']
        return message
    except errors.HttpError, error:
        print 'An error occurred: %s' % error

def ComposeEmail():
    # build gmail_service object using oauth credentials...
    to_addr = 'Mary Smith <[e-mail]>, [e-mail], Who? <[e-mail]>'
    from_addr = '[e-mail]'
    message = CreateMessage(from_addr,to_addr,'subject text','message body')
    message = SendMessage(gmail_service,'me',message)

Answer 1

As James says in its comment, you shouldn't waste time trying to use Gmail API when Python has excellent documented support for using SMTP : email module can compose message including attachements, and smtplib sends them. IMHO you could use Gmail API for what works out of the box but should use the robust modules form Python Standard Library when things go wrong.

It looks like you want to send a text only message : here is a solution adapted from the email module documentation and How to send email in Python via SMTPLIB from Mkyong.com:

# Import smtplib for the actual sending function
import smtplib

# Import the email modules we'll need
from email.mime.text import MIMEText

msg = MIMEText('message body')
msg['Subject'] = 'subject text'
msg['From'] = '[e-mail]'
msg['To'] = 'Mary Smith <[e-mail]>, [e-mail], "Who?" <[e-mail]>'

# Send the message via Gmail SMTP server.
gmail_user = '[e-mail]'
gmail_pwd = 'yourpassword'smtpserver = smtplib.SMTP("smtp.gmail.com",587)
smtpserver = smtplib.SMTP('smtp.gmail.com')smtpserver.ehlo()
smtpserver.starttls()
smtpserver.ehlo
smtpserver.login(gmail_user, gmail_pwd)
smtpserver.send_message(msg)
smtpserver.quit()

Answer 2

See also User.drafts reference - error"Invalid to header"

Apparently this bug was recently introduced in Gmail API.

Answer 3

Getting "Invalid to header" when sending with multiple recipients (comma delimited) in a single header was a regression that was fixed on 2014-08-25.