## The problem
Issue twilio/twilio-python#714 (closed, 8 comments): <!-- If this is a feature request, make sure you search Issues for an existing request before creating a new one! Please utilize the template below to help us resolve your issue. Note that many issues can be resolved by updating to the latest version. --> ### Issue Summary We're using the twilio-python library to send out thousands of SMS messages concurrently using Python's concurrent features library.

## The fix
'Connection pool is full' warnings come from your own ThreadPoolExecutor sizing, not twilio-python: urllib3's default pool size is 10, so set max_workers to 10 or less in your ThreadPoolExecutor, or customize pool behavior per the urllib3 advanced usage docs.

## Notes
Thread: https://github.com/twilio/twilio-python/issues/714. Verified against the closed issue and the maintainer/accepted answer there.