When lead emails need to be re-sent, a new toolbar action is available as shown below.
Simply check the box next to the leads that need re-sending, and click Re-send.
After clicking Re-send:
The leads, or lead notifications, will be re-sent.
The date for the lead will not change
Any configured "Thank you" message will not be re-sent
Triggers to send to Salesforce and Hubspot will not be re-run
Webhooks will not be re-run
If a lead has been re-sent, it will be indicated in the lead details, (click the binocular icon as shown above) and Resend Logs are shown at the bottom of the form.