An email header is the technical section at the start of a message. It includes fields such as From, To, Date, and Subject. Mail servers can add details such as Received fields that record transport hops. Email clients typically show only a selection of these fields in the inbox.
Which fields are useful?
Reply-To can specify a different address for replies. Received fields help trace the route of the message. Authentication-Results can report checks that a mail server performed. To interpret a field, consider which server added it.
Example of a delivery delay
If a newsletter arrives late, open the original message in your email client. Timestamps in several Received fields can help you identify where time passed between transport hops. Before sharing a header, check whether it contains personal addresses or internal details.
