I've written a sheduled batch apex class that I wasnt to run every day and send out an email to every user that has a custom Action object record that has passed its "Due Date". I have written the code below but the sendEmail method just throws an exception every time and despite catching it, the error doesnt really say anythinf useful. My code is below:

global class ActionOverdueNotification implements Database.Batchable<sObject>, Schedulable, Database.Stateful {

    //Variable Section
    global FINAL String strQuery;
    global List<String> errorMessages = new List<String>();
    
    global ActionOverdueNotification() { 
        this.strQuery = getBatchQuery();
    }
    
    //Returns the Query String to Batch constructor to fetch right records.
    private String getBatchQuery() {
        String strQuery = 'SELECT Id, Due_Date__c, Owner_Email__c FROM Action__c WHERE Due_Date__c < TODAY'; 
        return strQuery;
    }
    
    //Batch Start method
    global Database.QueryLocator start(Database.BatchableContext BC) {
        return Database.getQueryLocator(strQuery);
    }

    //Batch Execute method calls findCostForWoD method
    global void execute(Database.BatchableContext BC, List<sObject> scopeList) {
        System.debug(LoggingLevel.INFO, '== scopeList size ==' + scopeList.size());
        
        List<Action__c> actList = (List<Action__c>) scopeList;
        if(!actList.isEmpty()) { 
            List<Messaging.SingleEmailMessage> mailList = new List<Messaging.SingleEmailMessage>();
            EmailTemplate et=[Select id from EmailTemplate where name = 'Action Template' limit 1];
            for (Action__c act : actList)
            {               
                
                Messaging.SingleEmailMessage message = new Messaging.SingleEmailMessage(); 
                String[] toAddresses = new String[] {act.Owner_Email__c};
                Message.setTargetObjectId(act.id);
                Message.setSenderDisplayName('System Admin');
                Message.setTemplateId(et.id);
                Message.setToAddresses(toAddresses); 
                Message.SaveAsActivity = false;
                mailList.add(Message);
                
            }
            if(!mailList.isEmpty()) {
                try{
                    Messaging.sendEmail(mailList);
                }
                catch (Exception ex) {
                    errorMessages.add('Unable to send email: '+ ex.getStackTraceString());
                }
            }
        }
    }  

    //Batch Finish method for after execution of batch work
    global void finish(Database.BatchableContext BC) { 
        AsyncApexJob aaj = [Select Id, Status, NumberOfErrors, JobItemsProcessed, MethodName, TotalJobItems, CreatedBy.Email from AsyncApexJob where Id =:BC.getJobId()];
        
        // Send an email to the Apex job's submitter notifying of job completion.
        Messaging.SingleEmailMessage mail = new Messaging.SingleEmailMessage();
        String[] toAddresses = new String[] {aaj.CreatedBy.Email};
        mail.setToAddresses(toAddresses);
        mail.setSubject('JOB Salesforce Send Notification Batch: ' + aaj.Status);
        String bodyText='Total Job Items ' + aaj.TotalJobItems + ' Number of records processed ' + aaj.JobItemsProcessed + ' with '+ aaj.NumberOfErrors + ' failures.\n';
        bodyText += 'Number of Error Messages ' + errorMessages.size() + '\n';
        bodyText += 'Error Message' + String.join(errorMessages, '\n');
        mail.setPlainTextBody(bodyText);
        Messaging.sendEmail(new Messaging.SingleEmailMessage[] { mail });
    }
    
    //Method which schedules the ProductDownloadBatch
    global void execute(SchedulableContext sc) {        
        ActionOverdueNotification snInstance = new ActionOverdueNotification();
        ID batchprocessid = Database.executeBatch(snInstance);
    }
}

The error message is as follows:

Total Job Items 1 Number of records processed 1 with 0 failures.
Number of Error Messages 1
Error MessageUnable to send email: Class.ActionOverdueNotification.execute: line 45, column 1

Any ideas what I'm doing wrong?
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