Missing `send_each_at` option

[prayashm]

Issue Summary

Unable to use send_each_at option for scheduled emails as documented here:
https://sendgrid.com/docs/for-developers/sending-email/scheduling-parameters/#send-each-at

I intend to send mails to people at a fixed time in their timezone e.g. 10am IST and 10am GMT.

Steps to Reproduce

1. Send with mail.send_each_at = [1620766504, 1620767504]
2. The emails come instantly, instead of at the scheduled time

Code Snippet

mail = Mail(
	from_email=From('from@example.com'),
	to_emails=[To('IST@example.org'), To('GMT@example.org')],
	is_multiple=True,
)

mail.send_each_at = [1620766504, 1620767504]

client.send(mail)

Exception/Log

# no exception, code executes successfully.

Technical details:

• sendgrid-python version: 6.6.0
• python version: 3.7.9

[thinkingserious]

Hello @prayashm,

We have not implemented this feature as part of the mail helper, so I'm leaving this open for consideration. This issue has been added to our internal backlog to be prioritized. Pull requests and +1s on the issue summary will help it move up the backlog.

In the mean time, you can build the call without using the mail helper (full example).

With best regards,

Elmer