The man page of bash states: MAILCHECK Specifies how often (in seconds) bash checks for mail. The default is 60 seconds. When it is time to check for mail, the shell does so before displaying the primary prompt. If this variable is unset, or set to a value that is not a number greater than or equal to zero, the shell disables mail checking. Checking for mail remains enabled when MAILCHECK is set to zero. Setting MAILCHECK to -1 disables the mail check (or at least the message that you have new mail).
This package has changed ownership in the Fedora Package Database. Reassigning to the new owner of this component.
MAILCHECK=0 is supposed to keep the mail check enabled, just read the sentence one more time perhaps. Let me rewrite part of that man page for you in pseudo-code: if $MAILCHECK >= 0 MAILCHECK_ENABLED = true; else MAILCHECK_ENABLED = false;