You could use email for a direct dispute, but I caution against it.
The implementing rules for the direct dispute process go to lengths defining the appropriate address for receipt that compels a furnisher to investigate a direct dispute.
Electronic submission is not one of those unless the furnisher has directly informed you that they will accept disputes in that manner. That has obviously not occured, so you run the risk of no reply with no statutory date of the direct dispute.
The rules compel investigation if sent to the mailing address provided in your credit report, or their publicly available business address.
Use of email might also restrict the completeness of supporting documentation you may wish to provide.
