Have a look at the mailsender.py file to understand how emails are being sent.
Make necessary changes in the file to include attachments in the emails.
Try keeping the protocol to SMTP. I have added another issue to migrate away from the protocol. If you need to change the protocol, solve #3 first and then head back to solving #2.
Adhere to the Contribution section in the README, do not submit PRs from the master branch.
Have a look at the mailsender.py file to understand how emails are being sent.
Make necessary changes in the file to overcome SMTP mail sending limits and speed.
Try changing the protocol away from SMTP. Else if you are sticking with SMTP, make sure to increase the speed of sending mails. Also, try to work around the mail sending limits.
Adhere to the Contribution section in the README, do not submit PRs from the master branch.