This has been reported by many users from around the world that they are facing issue while sending email with attachment.
Gmail is down: Many users from Paksitan, India, Japan and from many other countries are reporting about the outage of gmail. DownDetector showing that the email sending problem especially with the attachments has been faced by many users not from just India, Japan, Austraila and also from other parts of the world.

This scanior of Gmail Down (outage) was verified by wirewag and found that the downtime is real and gmail is not letting users to send the email. People using even paid accounts of Gsuite are also facing this issue.

Such type of widespread issue has been reported for Gmail second time in last two months. In previous month of July many reports were reported by the users that they were unable to login to thier account.
Hopefully this issue would be solved by the Gmail administration very soon.