Re: [Fetchmail-users] Working around "Bad sender address syntax" error?

[Matthias A. <mat...@gm...>]

Am 09.09.2014 um 15:17 schrieb Daniel Barrett:
> 
> I use fetchmail to retrieve email from an IMAP server every five
> minutes, passing it to a local postfix process on my home Linux box
> for delivery. The problem: sometimes an email has an invalid "From"
> line (usually spam), like this one with leading hyphens:
> 
>   From: "- Some Dumb Spammer" <-Du...@ex...>
> 
> In this case, when fetchmail retrieves the email, the local postfix
> process raises an error:
> 
>   fetchmail: SMTP error: 501 5.1.7 Bad sender address syntax
> 
> This error causes fetchmail to leave the bad email sitting on the IMAP
> server, even when my .fetchmailrc file specifies "nokeep". As a
> result, fetchmail re-downloads it every five minutes. Repeat
> forever... or until I manually delete the bad email from the IMAP
> server.

Daniel,

Older fetchmail versions promised to never delete mail from the server
that was not reported as delivered by its SMTP/LMTP server or MDA, and
since v6.3.10, fetchmail lives up to this promise.

> What's the best way to break these loops automatically, either
> deleting or delivering the bad email, without opening a security hole
> (e.g., permitting leading hyphens)?

I see at least three options:

1. Leading hyphens are only a security risk if you are using scripts
that would feed them to utilities that do not understand "--" to mark
the end of options, or without these "--".  If you're sure you're safe,
you can permit them.

2. If you prefer to delete permanently undeliverable messages (those
that elicit error codes 500 and above), use --nosoftbounce on the
command line, or "set no softbounce" in the rcfile.  Details in the
manual page.

3. If you prefer to delete messages with particular error codes, see the
manual page about the antispam option, see Rob MacGregor's message for a
reference.

Best,
Matthias