Manual:$wgPasswordReminderResendTime

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Email settings: $wgPasswordReminderResendTime
Minimum time, in hours, which must elapse between password reminder.
Introduced in version:	1.9.0 (r17217)
Removed in version:	still in use
Allowed Values:	(integer)
Default Value:	24

Other settings: Alphabetical | By Function

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Minimum time, in hours, which must elapse between password reminder emails for a given account. This is to prevent abuse by mail flooding.

In a test server, I try a very small time, like "0.1" for test my mail server configuration; and it RUN PERFECT!!! In production server, leave the correct value.