Which module of the SMS gateway is responsible for caching and retransmitting messages?

Message caching module.

According to the CSDN blog query, the main responsibility of the message cache module is to receive and temporarily store SMS messages received from various sources. These messages may be sent from different senders, or through transmitted through different channels.

Once the message caching module detects a network or channel failure, or does not successfully send messages within the specified transmission timeout period, it will be responsible for caching these messages and making resend attempts.