Email Header: "Return-Path" Contains Unknown Address

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 account@example.com:

    Return-Path: SRS0=OVdk=H5=example.com=m
    ax.account@srs2.ionos.co.uk