Is To: an Array or List?

[PythonLinks]

Message To: has to be a string.
message['To'] = 'Paul paul@example.com, Tres tres@example.com'

But delivery.send
delivery.send('chris@example.com', ['paul@example.com', 'tres@example.com'],
message)
Has to be an array.

It took a few hours to figure that out
It would be good if the software actually tested to make sure that one is a string, and the other an array.

[mmerickel]

I would accept a PR that ensured that the toaddrs arg was a non-string iterable or some improved documentation.