Gmail Account gets temporarily locked-up due to unusual usage

[decoded-cipher]

Best Guess:
As a large number of emails gets created within a very short span of time, Gmail's security algorithm detects this as an anomaly and temporarily suspends the activities of the same to protect the system.

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It has also been noticed once in a while, the errors related to "Too many requests" and errors with Status code 421 from Gmail (SMTP)