If you do not know the email address entered under Return-Path in the email header, this email may have been forwarded to your address through another 1&1 IONOS mailbox.
If a 1&1 IONOS mailbox forwards an email, the 1&1 IONOS mail system stores a coded entry in "Return-Path" according to the so-called Sender Rewriting Scheme(SRS):
- The SRS ensures that the original sender of a forwarded email remains recognisable by an entry in the email header. Undeliverable messages can be sent to the original station.
- The entry is created according to the following pattern: SRS0=HHH=TTT=hostname=local-part@domain, where HHH is a hash and TT is a timestamp;
in the following example the email was originally sent from firstname.lastname@example.org: