1. Create an Email Template.
2. Note down the Email Template Id.
3. Create a Contact record with the Name “Do Not Delete”.
4. Use the dummy Do Not Delete Contact Id in the setTargetObjectId() method.
5. Set setTreatTargetObjectAsRecipient as false to avoid sending email to the Contact record. setTreatTargetObjectAsRecipient as false will ignore the setTargetObjectId and it won’t send an email to it.

Sample Trigger:

trigger AccountTrigger on Account ( after insert, after update ) {  
  
    Contact objCon = [
        SELECT Id
        FROM Contact
        WHERE Name = 'Do Not Delete'
        LIMIT 1
    ];
    List < Messaging.SingleEmailMessage > listMsgs 
        = new List < Messaging.SingleEmailMessage > ();  
  
    for ( Account acc : trigger.new ) {  
  
        Messaging.SingleEmailMessage msg 
            = new Messaging.SingleEmailMessage();  
        msg.setWhatId( acc.Id );  
        msg.setTemplateId( 
            '00XHo000001Zrvh' 
        );//Id of the Email template  
        msg.setToAddresses( 
            new List < String > { '[email protected]' } 
        );  
        /*
         * Setting Contact Id to avoid error. 
		 * It won't send the email due to 
		 * setTreatTargetObjectAsRecipient
		*/  
        msg.setTargetObjectId( objCon.Id ); 
        msg.setTreatTargetObjectAsRecipient( false );   
        listMsgs.add( msg );  
  
    }      
  
    Messaging.sendEmail( listMsgs );  
  
}