Lipid transporter that specifically mediates export of sphingosine-1-phosphate in red blood cells and platelets (PubMed:29045386). Sphingosine-1-phosphate is a signaling sphingolipid and its export from red blood cells into in the plasma is required for red blood cell morphology (By similarity). Sphingosine-1-phosphate export from platelets is required for platelet aggregation and thrombus formation (By similarity). Mediates the export of different sphingosine-1-phosphate (S1P) species, including S1P(d18:0) (sphinganine 1-phosphate), S1P (d18:1) (sphing-4-enine 1-phosphate) and S1P (d18:2) (sphinga-4E,14Z-dienine-1-phosphate) (Probable). Release of sphingosine-1-phosphate is facilitated by a proton gradient (By similarity). In contrast, cations, such as sodium, are not required to drive sphingosine-1-phosphate transport (Probable). In addition to export, also able to mediate S1P import (By similarity). Does not transport lysophosphatidylcholine (LPC) (Probable). {ECO:0000250|UniProtKB:Q3T9M1, ECO:0000269|PubMed:29045386, ECO:0000305|PubMed:29563527}. This is the function of MFSD2B (MFSD2 lysolipid transporter B, sphingolipid, ENSG00000205639).