Partly disabled delivery notification? How did they do that?

Richard G

Verified User
Joined
Jul 6, 2008
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12,554
Location
Maastricht
Just out of curiosity I would like to ask this.

A Dutch ISP (Telfort and maybe others) have disabled the DSN on their servers or at least it looks that way.
This is what was happening:
Customers sending an e-mail client could configure that they would get a delivery notification if the mail was delivered to the mailbox (no not the "mail is read" notification that's something else).
This worked until shortly.

Now they disabled this option and I know this can be done, but they did it in a way I don't understand. This is in a pop3 situation, not tested with imap.
Customers sending an e-mail client will not get the delivery notification anymore.
The same customer sending an e-mail with the webmail of the ISP -do still- get the delivery notification.
The same customer sending an e-mail with the webmail of the ISP but then retrieve their mail with the e-mail client also receive this delivery notification.

So when using webmail, delivery notification is send to the mailbox, but when using an e-mail client to send mail it's not.

The ISP says they disabled this "for security reasons". But I don't understand why they did not disable it completely, so on the MTA so it won't work with Webmail either.
And I don't understand why it's still working with webmail as webmail normally is directly connected to the mailbox on the server.

So I have 2 questions out of curiosity.
1.) Where have they blocked this option then? Is there an option to block delivery notifications in Dovecot or something? This would explain that it doesn't work with pop3 but does work with webmail.
2.) And if that's the case, where is the security improvement in that?
 
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