I have created a simple auto-covert lead trigger that works.  I upgraded it to attach to an existing account ID if that account was identified on a custom lookup field on the lead.  Now I want to upgrade it again to add to an existing contact if the lead email matches one of the emails from a contact record related to the account that was identified on the lead.  Here is my code and I am trying to figure out how to reference the lead email and the contact email in a SOQL query.  I know I also need to add a chunck of code to check and see if my results are blank but I need to figure out this SOQL thing first.

trigger AutoConvertLead on Lead (After Update) {
    for (Lead lead : Trigger.new) {
        if (lead.isConverted == false && lead.Qualification_Score__c>=6) //to prevent recursion
        {
            Database.LeadConvert lc = new Database.LeadConvert();
            lc.setLeadId(lead.Id);
            
            String oppName =  lead.Name;
            lc.setOpportunityName(oppName);
            
            LeadStatus convertStatus = [SELECT Id, MasterLabel FROM LeadStatus WHERE IsConverted=true LIMIT 1];
            lc.setConvertedStatus(convertStatus.MasterLabel);
            
            //If the account lookup field is filled out then it will merge to that account instead of creating a new one.
            if (lead.Account__c != null)
            {
                String ExistingAccount = lead.Account__c;
                lc.setAccountID(ExistingAccount);
            }

            if (lead.email != null)
            {
                String CurrentEmail = lead.email;
                String ExistingContact = [SELECT Id FROM Contact WHERE email = CurrentEmail AND AccountID = ExistingAccount LIMIT 1];
                lc.setContactID(ExistingContact);
            }
            
            Database.LeadConvertResult lcr = Database.convertLead(lc);
            System.assert(lcr.isSuccess());
        }
    }
}