External mail意思
"External mail" is a term used in the context of email communication to refer to messages that are sent or received from outside of an organization's internal email system. In other words, it refers to emails that come from or go to email addresses that are not part of the same company or organization.
For example, if you work for a company and you receive an email from your personal email account, or if you send an email to a friend who is not employed by your company, those emails would be considered external mail. Similarly, if you work for a company and you receive an email from a customer or a supplier who is not part of your company's email system, that email would also be considered external mail.