Firstly, it is very unlikely that an email that is not spam fails to arrive. In the rare event that it happens, the sender receives a message, in any case. The failure-rate of our spam filter is very low.

If the sending server is unknown to us, the email may arrive after a delay. First, we block all emails from unknown servers by (so-called) greylisting. The sending server generally tries again after a short time; we then take the email and note the server for future reference. We do this because spammers only rarely send an email twice. This blocks most spam.

Other reasons for non-received emails may be:

• The sending server did not successfully send the email.
• The sender did not enter your email address correctly.
• If you are waiting for a reply, you may have sent the email with an identity or an alias that is not correctly configured, such that nobody can answer emails from this particular sender.
• The email was classified as spam and the sender did not see the error email explaining that the message was not delivered.

Please make yourself known via support@posteo.de if an email has gone missing and this article does not help you locate it.