In Salesforce by using the Email Alert we can send the emails to whomever we want. For the email alert we need any one of the Email templates to send the Email successfully. Also We can add the Static Attachment to that template. Whenever we send mail by the Specific email template It will automatically send with attachment which we added in the Email template attachment.
This is the blog to attach a file to an email template and follow the steps to do lightning as well in classic.
In Salesforce Classic :
Step-1 : In setup, Search for the Classic Email Templates and click it.
Step-2 : Open the Email template for which one we need to add the attachment.
Step-3 : Once selected the Email Template, Bottom of the page we can see the Attachments Section. Click the Attach file Button.
Step-4 : Select the file which one wants to attach with this template.
To test this, Click the Send Test and Verify Merge Fields on the Same Page and send the test Email to Preview.
This is preview mail of the attachment :
In Lightning Experience,
Step-1 : Go to any object that has an Email publisher available.
Step-2 : Go to the Email tab.
Step-3 : Select the Email template that you wish to add an attachment to by clicking on the
Step-4 : Insert, create or update Template button.
Step-5 : Select Insert Template.
Click the Attach file button and select the file you wish to attach to the template.
If you would like to save this template with the attachment for future use, click Insert, create or update Template and select Save Template.
For more Blogs : How to Turn Off Salesforce Classic
For Reference : Click here