Such notice may be served personally or by mail, and if by mail it may be addressed to such master plumber at the address registered by him, but the failure of a master plumber to register will relieve the official or board who or which appoints the plumbing inspector from the requirement of giving notice of violation. Unless the violation is removed within three days after the day of serving or mailing such notice, exclusive of the day of serving or mailing, the official or board who or which appoints the plumbing inspector may proceed according to law.