You may use a telnet program to connect manually to the server. Then you can read the plain text mail and see what is wrong, optional copy the content using the clipboard, and optional delete the malformed mail:
> telnet <server> 110
user <user name>
+OK 2 1980
+OK 2 messages (1980 octets)
top 1 10
<First 10 lines of mail no. 1>
<Content of mail no. 2>
+OK message 2 deleted
The ".CRLF" sequence is send by the POP server to indicate the end of data. See RFC 1939 [^
], "3. Basic Operation", 4th text block, about this and how text containing the termination sequence is handled. It does not matter if the mail text contains this sequence.
The problem is sourced by the mail providers SMTP server code or setup which accepts an invalid mail (such mails should be rejected), or by his local mail delivery procedure which may damage the message or insert invalid headers.