The problem is that the iPhone does not send a DELE command to the POP3 server to tell it to delete the email, even if the iPhone is configured to remove email from the server immediately.
A POP3 connection from Outlook. The DELE command tells the server to delete the email from the server.
+OK
CAPA
-ERR
USER <redacted>
+OK
PASS <redacted>
+OK
STAT
+OK 1 4455
UIDL
+OK
1 8ec569e77d6858a9
.
LIST
+OK
1 4455
.
RETR 1
+OK
Received: from <redacted>
DELE 1
+OK
QUIT
+OK
From an iPhone. Notice that it does not send a DELE command.
+OK
USER <redacted>
+OK
PASS <redacted>
+OK
UIDL
+OK
1 cb3a6c8955dd1d38
2 bb6184fa9ae81ed4
3 LIST
+OK
1 29560
2 5010
3 2984
4 26851
5 9141
RETR 14
+OK
Received: <redacted>
QUIT
+OK
The iPhone's POP3 support is plainly broken, but they are giving my sister-in-law the run around telling her that the problem is on the server. From what I read in previous replies, I think they are trying to dance around the fact that their POP3 is broken, and trying to get her to use IMAP.
Sometimes IMAP is not an option, and sometimes (depending on how you want to use your email) it is not a good option.
I think it's time for Apple to stop being lazy and fix their POP3 support.
I *TOLD* her to get an Android phone, but did she listen to me? No! At least POP3 support works right on Android. 🙂
