Sent email returned in my inbox

Support
1

I sent an email to someone (existing) and the mail returned few seconds later in my inbox without telling any reason why it returned.

Any idea what happened?

2

A few more details would be useful: device type and operating system version, version of K-9 Mail, POP3 or IMAP, any customized email headers, maybe a log. These are not a guarantee that someone will be able to diagnose your issue, but the more information provided, the more likely assistance could be forthcoming. Thanks.

3

So it’s the latest Android version 17, K9mail version 23.1. IMAP/POP set on the mail Server.

All other emails sent to different users are working fine.

4

Do you have POP3 on this server or IMAP? I am not aware that you could use both on a single server. A log might be useful, although I have never used that facility, so perhaps someone more experienced than me can assist.