Reducing SPAM – A Look at SRS (Sender Rewriting Scheme) for 1&1 E-Mail Servers

In April 2015, 1&1 made a change to the e-mail system, which may lead to a changed behavior for certain web hosting customers when sending e-mails.

From now on, the 1&1 mail servers will only use the Sender Rewriting Scheme for forwards. So far, SRS has also been used when a sender address was freely selected and the sending domain was not registered with 1&1. By eliminating SRS in these cases, it can happen that certain recipients classify as spam the e-mails that they have previously accepted due to SRS.

SRS Adjustments and Effects on E-Mail Delivery

If you send e-mails from your PHP, Perl or .NET application with a sender address not registered with 1&1, the owner of the sender address (e.g. Google for can prevent that the e-mail reaches the recipient.

This takes place to protect against SPAM.

You can change the sender address for your e-mails, so that you use either your own one, registered with 1&1 domains, or a package such as Swift Mailer, and directly deliver the e-mails to the desired server of the sender address.

In Detail: Mail Server Configuration and SPAM Protection with SPF and SRS

With the help of SPF, a domain owner can restrict the mail servers over which the e-mails with his sender address (e.g. may be sent.

For this purpose, in the DNS system for the sender domain (in the example „“), a so-called SPF record is entered with the mail servers allowed for the mail delivery. The recipient of an e-mail can make sure by checking the SPF record that the e-mail was delivered over a valid mail server.

Because many SPAM e-mails are sent by other routes, e.g. from so-called BOT networks, the recipient can detect them, identify a SPAM e-mail as such, and categorize it accordingly or even refuse to receive it.

How to act exactly in this case is defined by the SPF information stored in the DNS and therewith, the owner of the sender address.

Fixing the limitations of SPF: SRS

The SPF procedure reaches its limits when e-mails must be passed by automatic forwards from a recipient address to another one. Since usually the sender address is not changed, the recipient of the e-mails finds out when checking the SPF information that the sending system is not in the list of allowed systems. The system would treat the e-mail as SPAM. This undesirable behavior at forwards can be prevented by means of SRS.

Mail servers check by means of SRS whether a SPF examination of the sender address occurred, was positive and therefore, a further examination by the recipient must no longer be performed. This is how SPAM can be reduced better and more effectively.

In order to not deteriorate the effectiveness of SPF, SRS should only be used for forwarded e-mails. 1&1 has now implemented this configuration in the mail server.

Impact on E-Mail Delivery from PHP, Perl and ASP.NET Applications

Web hosting customers have the possibility to send e-mails from their applications (see 1&1 Help Center). Most PHP and ASP.NET applications already have such a function. Often, a free sender address can be selected. Customers using as sender address one of their domains registered with 1&1 are not affected by the configuration change.

Customers using another sender address such as „“, „“ or „“ have also been dealt with in the past by SRS. Thus, e-mails with these sender addresses have been dealt with on the recipient page as if they had successfully passed the SPF examination, even though this was not the case.

1&1 respects the wish of domain owners, explicitly limiting by means of the SPF records the mail servers over which e-mails with their sender addresses can be delivered. Therefore, we no longer use SRS in case of a freely selected sender address. This can cause that e-mails with sender addresses not registered with 1&1 are treated by the recipient as spam or completely rejected. This behavior is the wish of the owners of these domains and cannot be influenced by 1&1.

What Can I Do as a Customer?

You must do nothing if you only send e-mails with sender addresses registered with 1&1. 1&1 automatically considers the SPF record provided by you in the DNS.

If you use other sender addresses such as „“, „“ or „“, we recommend that you check in random samples whether your emails are received as usual. If you detect that some recipients classify your e-mails as spam, we recommend this solution:

  • Change the sender address and select an address with a sending domain that you registered with 1&1.


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