Why does the Gmail API return an "invalid to header" error while my API had been working fine for weeks?

Question

Using the quickstart guide for the Gmail API with Python, I get an 400 error "Invalid to header" when trying to create a draft.

I have been using my little script for a few weeks and it worked perfectly fine to create invoice drafts in bulk, until one day it just stopped working even though I had not modified any code.

This is the error I get:

   1 file(s) copied.
Traceback (most recent call last):
File "quickstart.py", line 223, in <module>
main()
File "quickstart.py", line 207, in main
create_draft(service, 'me', message_body)
File "quickstart.py", line 134, in create_draft
draft = service.users().drafts().create(userId=user_id, body=message).execute()
File "C:\Users\$User\AppData\Local\Programs\Python\Python37-32\lib\site-packages\googleapiclient\_helpers.py", line 130, in positional_wrapper
return wrapped(*args, **kwargs)
File "C:\Users\$User\AppData\Local\Programs\Python\Python37-32\lib\site-packages\googleapiclient\http.py", line 842, in execute
raise HttpError(resp, content, uri=self.uri)
googleapiclient.errors.HttpError: <HttpError 400 when requesting https://www.googleapis.com/gmail/v1/users/me/drafts?alt=json returned "Invalid to header">

When I got this error for the first time, I deleted the credentials file and downloaded a new one. But now this solution doesn't seem to work anymore.

Does the credentials.json file expire after some time?

What's the "to" header you are using in the email and has it changed? Could you share the relevant sections from quickstart.py? — payne

Vova Vova · Accepted Answer · 2019-01-21T18:14:48

i got the same error when tried to send email to "@something2" (normal email is something1@something2, you might miss "something1", e.g your email is invalid)

Error does not happens if you put normal email, so you should validate your input.

Why does the Gmail API return an "invalid to header" error while my API had been working fine for weeks?

1 Answers