How does someone set their email address to "unreachable / doesn't exist"?
You know the feeling. You mistype the recipient's email address and get an error message (Mailer Daemon).
What's confusing me, though, is that I sometimes send emails to email addresses I know exist, and sometimes (only sometimes) I can't get through, and I can tell because I get an error message like this.
Either they are stressed and therefore do not want emails to arrive, or they want to make certain people believe that the email address does not exist…
I'm really not making any typos. Sometimes I get through to these addresses, sometimes I get an error message right away, and sometimes it takes 45 minutes…
How do they do that?
After receiving an email, i.e. seeing the email, can you still ensure that the sender receives an error message like this?
Sorry for the long text, complicated.
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A temporary inaccessibility can have many reasons, you must pay attention to which of the two MTAs refers to the error message.
If the sending MTA cannot resolve the name of the receiving MTA, the situation is different than, for example, a temporary disturbance in the receiving MTA. There are really many possibilities. Thus, for example, the connection to an external DB server can be disturbed so that the information about the mailbox can not be found.
Then there’s something like Greylisting, then a mail is first rejected from principle. A normal MTA tries to deliver again after some time. If necessary, the sending MTA generates a message about temporary inaccessibility. If the second delivery attempt has enough distance from the first one, the mail will be mowed to the recipient.
etc. .
If it lasts the sending MTA too long (too many attempts) then it creates a final inaccessibility message.
By line it takes details from the report and, if necessary, the headers to understand why an email did not arrive.
And yes, of course you can also use the filter to make sure that mails based on ceremonies are rejected as inaccessible, although the destination address is correct. And such filters can also be automated. Too much spam from an IP, source IP is set in filter. After relaxation time, it is removed again.
The mail you get is not coming directly from the sender but from the mail server itself. It is therefore returned from the server to you within the protocol (IMAP or POP3). This is not caused by users, but because the server really cannot find the address. In my knowledge, it is not easy to fly, as a normal consumer: in a typical mail provider it is not quite possible. I guess you just tipped yourself.
No, I really didn’t tip me
If someone drives his/her own mail server, he could take the addressed recipient, e.g. from the list of virtual recipients (these are those who do not need or have an account on the computer with the mail server). If he wishes to send the addresseee back to the mail, he will receive him in it again.
Such virtual receivers can also specify other receivers on the same server for their incoming mail. If these are temporarily not existent, the mail to the original user is also rejected as “receiver not known”.