I believe RFC2646 specifies the line wrapping mechanism that is vexing you. Its intent is to describe
[...]a format which is in all significant ways Text/Plain, and therefore is quite suitable for display as Text/Plain, and yet allows the sender to express to the receiver which lines can be considered a logical paragraph, and thus flowed (wrapped and joined) as appropriate.

I believe these messages should include "Format=Flowed" in the "Content-Type:" header line. The clues to reforming paragraphs are mostly hidden in the whitespace.

On line lengths, RFC5322 specifies (section 2.1.1):

Each line of characters MUST be no more than 998 characters, and SHOULD be no more than 78 characters, excluding the CRLF.

This is not a POP3 issue.

In reply to Re: POP3 and long lines (Mail::POP3Client) by eye
in thread POP3 and long lines (Mail::POP3Client) by Anonymous Monk

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