You can switch off a message using Off[symbol::tag]. You can switch on a message using On[symbol::tag].
Between any two successive input lines, Mathematica prints a message with a particular name at most three times. On the last occurrence, it prints the message General::stop.
Off[General::stop] makes Mathematica not stop repeating messages.
During the evaluation of a particular input line, names of messages associated with that input line are appended to the list $MessageList, wrapped with HoldForm. At the end of the evaluation of the n input line, the value of $MessageList is assigned to MessageList[n].
Message[mname, e1, e2, ...] is printed as StringForm[mess, e1, e2, ...] where mess is the value of the message mname. Entries of the form `i` in the string mess are replaced by the corresponding ei.
Given a message specified as symbol::tag, Message first searches for messages symbol::tag::langi for each of the languages in the list $Language. If it finds none of these, it then searches for the actual message symbol::tag. If it does not find this, it then performs the same search procedure for General::tag. If it still finds no message, it applies any value given for the global variable $NewMessage to symbol and "tag".
If you specify a message as symbol::tag::lang, then Message will search only for messages with the particular language lang.