B757-200
Dispatch Dispatcher
Communication Breakdown
Aircraft Equipment Problem Less Severe; Deviation / Discrepancy - Procedural Maintenance; Deviation / Discrepancy - Procedural MEL / CDL; Deviation / Discrepancy - Procedural Published Material / Policy; Inflight Event / Encounter Fuel Issue
Flight Crew Diverted; Flight Crew Landed As Precaution
Human Factors; Procedure
Planned flight as normal; no limiting MELs were attached to the aircraft at any point during planning.  I received a call from the crew at asking for clarification that MEL XX-XX-X-1 meant that center tank fuel was unusable; I confirmed this was the case; that this MEL means that both center pumps are INOP and that any fuel in the center is trapped; I thought it was a generic question and didn't question the MEL on this specific flight.  I was advised by Dispatcher X that he believed the flight departed below minimum fuel; I brought up the [planning] and the fuel I had planned it with was below the level at which fuel is added to the center tank; this immediately raised flags and I attempted to contact ZZZ Tower to stop the aircraft from taking off; however they said clearance had already been given and the aircraft was rolling.  I believe the aircraft departed with approx 24.7 usable fuel with a MIN TAKEOFF fuel of 27.0.  After takeoff and at a safe altitude; I ACARSed the crew asking them to confirm the fuel available in their main tanks only; I determined this fuel was not sufficient to make it to RFD and advised the dispatch lead.  The crew agreed that a tech stop was in the best interest of safety and it was decided that ZZZ1 was a suitable gateway for this; the flight was diverted to ZZZ1 to add fuel.  Unfortunately; at no point during the pre-planning or planning stage of this flight; did I receive a call from Maintenance Control advising the MEL was being added; nor did the crew request an amended release before blockout advising that the MEL was not on their paperwork and thus not considered for the flight.  The call was a routine call in which I thought the crew was just asking for interpretation of a MEL.I would suggest to Maintenance Control that they advise all dispatchers that have that tail assigned of any MELs being added; unfortunately we don't always have the aircraft on its previous leg and thus when they advise one dispatcher of an MEL being added; the next dispatcher does not receive this information.
Dispatcher reported that a flight departed without the minimum required fuel due to a miscommunication about an MEL.