Hello,
The General Instruction of the Roman Missal states:
D. THE CONCLUDING RITES
- The concluding rites consist of
a. Brief announcements, if they are necessary;
b. The priest’s greeting and blessing, which on certain days and occasions is enriched and expressed in the prayer over the People or another more solemn formula;
c. The dismissal of the people by the deacon or the priest, so that each may go out to do good works, praising and blessing God;
d. The kissing of the altar by the priest and the deacon, followed by a profound bow to the altar by the priest, the deacon, and the other ministers.
The recessional hymn is not a part of the concluding rites or the Mass proper.