Answer: There are at least 3 more epistles of Paul mentioned in the New Testament. One epistle is for the Laodiceans, an additional epistle for the Corinthians and also for the Ephesians.
The Epistle to the Laodiceans, was mentioned by Paul on his closing address to his epistle to the Colossians (Colossians 4:16). The church of Laodicea which was in Syria; was also mentioned by John in the book of Revelation (Revelation 3:14-22). Paul exhorted the saints in Colossae, an ancient city of Phrygia; to let his epistle to be circulated on the church of Laodicea. While he expected that the Laodiceans; who also received another letter from him, will do the same to the Colossians.
The other Epistle to the Corinthians was probably the first letter of Paul to the church of Corinth, an ancient city in Greece. If it was included in the canonized books of the New Testament, it will take the place of the 1 Corinthians while the two other epistles will be moved respectively as the second and the third. Not much information was known about this letter, except that Paul in one line described it as an epistle he wrote to warn the saints of Corinth to stay away from people who practiced fornication (1 Corinthians 5:9).
Lastly the Epistle to the Ephesians was also an earlier letter written by Paul other than the one included in the canon. It was written for the church of Ephesus; an ancient city in Greece that was also mentioned in the book of Revelation (Revelation 2:1-11). This epistle contains a profound understanding of Paul about the mystery of Christ as revealed to the holy Apostles and prophets by the Spirit (Ephesians 3:3-5).
Among these three non-canonical epistles only the Epistle to the Laodiceans has a known copy existed today. However the date of its existence and the certainty of its authorship were still questionable. Also, its contents were mostly copies of some of Paul's epistles in the Bible. Thus, it doesn't have much information that can be used for edification to some issues in those days.
