[Tickets #5245] infinite mail loop with forward rule

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Ticket URL: http://bugs.horde.org/ticket/?id=5245
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 Ticket             | 5245
 Created By         | alex at segv.de
 Summary            | infinite mail loop with forward rule
 Queue              | Ingo
 Version            | 1.0.1
 Type               | Bug
 State              | Unconfirmed
 Priority           | 2. Medium
 Owners             | 
+New Attachment     | procmail_forward.patch
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alex at segv.de (2007-04-11 09:07) wrote:

- User activates forwarding of emails
- Destination email is invalid, e.g. alex at segv.de;  (Note the semicolon
after the email address!)
- exim generates a bounce ("alex at segv.de;  malformed address: ; may not
follow alex at segv.de")
- this bounce is forwarded and bounces again. => infinite mail loop,
server goes down with out of memory after a few thousend bounces.

Possible fix: add "* !^FROM_DAEMON" to forward rule to exclude all
bounces, but that defeats the point of forwarding somewhat, if possible
important mails don't get through :/

Another idea: prevent user from entering syntactically invalid email
addresses. (What about undeliverable addresses?)

The attached patch implements the first idea.