I've recently added a couple of lines of code to a validation script I created in a trigger so that if a field is checked, after insert/update creates an email to be sent to me notifying me of the change. In the sandbox, the trigger works great and sends the email to me just once. However, in production the same trigger causes me to receive the email twice. Any thoughts?

Here's the email portion of the code:

String userName = UserInfo.getName();
String completeUser = UserInfo.getName() + ' (' + UserInfo.getUserName() + ')';
String triggerType;
				
if(trigger.isInsert) triggerType = 'adding';
if(trigger.isUpdate) triggerType = 'updating';
				        
String subject = userName + ' has overriden the Contact Validation script in Salesforce';
String plainTextHeader = completeUser + ' has overriden the Contact Validation script when ' + triggerType + ' ' + contactName + '\'s record in Salesforce. Here are matching records:\n';
String htmlHeader = '<h3><strong>' + completeUser + ' has overriden the Contact Validation script when ' + triggerType  + ' <a href=\'salesforceOrg' + contactId + '\'>' + contactName + '\'s</a> record in Salesforce. Here are matching records:</strong></h3><ul>';
String plainTextBody = '';
String htmlBody = '';
				
List<Account> a = [SELECT ParentId FROM Account WHERE Id =: branchId AND Home_Office__c != null];
firmId = a[0].ParentId;
				        
for (Contact c : [SELECT Id, Name, Account.Name FROM Contact WHERE Id !=: contactID AND Account.ParentId =: firmID AND Name =: contactName AND Active__c = True])
{
	Id matchId = c.Id;
	String matchName = c.Name;
	String matchCompany = c.Account.Name;
					          
	plainTextBody = plainTextBody + matchName + matchCompany + '\n';
	htmlBody = htmlBody + '<li><a href=\'salesforceOrg' + matchId + '\'>' + matchName + '</a> - ' + matchCompany + '</li>';
}
			        
String htmlFooter = '</ul>';
				
String plainTextMessage = plainTextHeader + plainTextBody;
String htmlMessage = htmlHeader + htmlBody + htmlFooter;
				        
Messaging.SingleEmailMessage mail = new Messaging.SingleEmailMessage();
String[] toAddresses = new String[] {'myemailaddress'};
mail.setToAddresses(toAddresses);
mail.setReplyTo('myemailaddress');
mail.setSenderDisplayName('Salesforce.com Contact Validation Override');
mail.setSubject(subject);
mail.setPlainTextBody(plainTextMessage);
mail.setHtmlBody(htmlMessage);
Messaging.sendEmail(new Messaging.SingleEmailMessage[] { mail });