The Contact Delete process can be slow for a large number of contacts. To expedite this process, the best approach is to stop the current delete process and delete smaller groups of contacts. This allows the system to handle smaller chunks of data more efficiently.
* Stop Current Process: Stopping the current large delete process helps avoid system overload and potential timeouts.
* Delete in Smaller Groups: By segmenting the contacts into smaller groups and deleting them in batches, the process becomes more manageable and faster.
1: Salesforce Contact Deletion Best Practices

To store only the first 4000 characters of the fields SMTPBounceReason and SMTPCode in a data extension, the developer should use the LEFT (C) SQL function. This function returns the specified number of characters from the beginning of a string.
Example:
SELECT SubscriberKey, LEFT(SMTPBounceReason, 4000) AS SMTPBounceReason, LEFT(SMTPCode,
4000) AS SMTPCode FROM _Bounce
References:
SQL LEFT Function
Salesforce Marketing Cloud SQL Reference

To determine the best identifier for subscribers across all channels, Contact Key (A) should be recommended.
The Contact Key is a unique identifier that can be used consistently across all channels, ensuring a unified view of the subscriber's interactions and data.
References:
Salesforce Marketing Cloud Contact Builder
Contact Key Overview

To expedite the process of deleting roughly 10 million subscribers using Contact Delete, the developer should change the Suppression value to a larger value (A). Increasing the suppression period helps in reducing the time taken for the deletion process as it allows the system to handle more deletions at once, thus speeding up the overall process.
References:
Salesforce Marketing Cloud Documentation on Contact Delete
Marketing Cloud Contact Deletion Best Practices

To trigger an SMS message to a subscriber using a form published on CloudPages, the developer should use therequestToken and messageContact REST API objects (D). These objects can be used to authenticate and send the SMS message programmatically when the form is submitted.
References:
* Salesforce Marketing Cloud MobileConnect API
* Salesforce Marketing Cloud REST API