Thanks to all for your answers,
I'll give the acl_ckeck_data a chance. The funny thing is that I checked
some free Mail providers like gmx, web.de, and so on
And Web.de was the only one that always created a warning mail to my
mailaccount, that someone wanted to use my mailaddress and whether I
want to allow it or not. Thats the reason I thought there must a way to
do so, too.
Greetings,
Sandra
Am 18.02.2013 16:43, schrieb Ian Eiloart:
On 17 Feb 2013, at 20:46, Deep Thought <[email protected]> wrote:
Dear Sir or Madam,
I am using Exim on my server and realized that any user can overtake a mail
address created by an user account. So it seems that for example, I can just
enter an Alias or even change my sender mailaddress for example in Thunderbird
to any mail addresses created by the account.
Yes, that's true.
Similarly, if I write a letter to anyone, I can put your address at the top of
the letter, or any address that I like to put. There's nothing that you, or
anyone else, can do to prevent that.
The only things that you can do to attempt to secure your email domain (and
hence addresses in that domain) are to publish SPF, DKIM and DMARC records.
Some recipient sites will check those records, including some large email
service providers. None of that will prevent forgery.
You can also use S-MIME or GPG/PGP to sign outgoing mail, but that only
protects you to the extent that recipients (a) expect it, and (b) have tools to
analyse the signatures.
There is no security check or a warning message like "Hey someone is using your
mailaddress".
How can I secure it? Is there any setting to change this behaviour? That the
owner of the mail address has to agree on using its mail address as an alias or
sender mail address from another account?
You can only do this if you know the sender is going to use your email server.
In that case you could, for example, create an ACL that requires that the
sender address be present in the from header.
Thanks in advance,
Sandra Mende
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