Don't 500 when the email doesn't map to a valid user ID.
Don't 500 when the email doesn't map to a valid user ID.

TribeMedia/synapse,iot-factory/synapse,iot-factory/synapse,TribeMedia/synapse,matrix-org/synapse,matrix-org/synapse,iot-factory/synapse,iot-factory/synapse,TribeMedia/synapse,matrix-org/synapse,matrix-org/synapse,iot-factory/synapse,matrix-org/synapse,TribeMedia/synapse,TribeMedia/synapse,matrix-org/synapse