https://www.btstories.com/2nd-letter-to-the-corinthians-1/

The church at Corinth didn’t respond well to Paul’s first letter, so he sailed across the sea and met with them. That didn’t go well either. He then sent them a very harsh letter—one that’s not included in the Bible. Titus returned with encouraging news on how they took it to heart and repented of their sins. Paul then sent this letter. He said:

May the grace and peace of our Lord Jesus Christ be with you.