I'm not sure what exactly. The thing is, I've got an email-message about 40k. The recipient can't view the message, he'll get a "Maximum execution time reached for mime.php" with a variable line number behind that. The line number is 824, 825 or 1453 or something like that, but it switches.
Now, one might assume something is wrong with the message. Since the message is quite long, it's not time efficient to go through all of it. So as a test, I wanted the message in my own inbox, so I could test between which lines things would break. I opened up a telnet session with localhost on port 25, told it it was getting MAIL FROM: me and RCPT TO: was my address of the webmail server. Then I parsed the complete message.
I logged into Squirrelmail and tried the message... and it worked. Without any trouble, I got the message on my screen in less than a second. I thought I could simply diff the two mail-sources to see what's wrong.
Since we're using Cyrus IMAP, we could identify the messages and diff them. The diff didn't produce anything spectacular, but for completeness, I'll put them here, a bit anonymised.
< From email@example.com
< Return-Path: <firstname.lastname@example.org>
> Return-Path: <email@example.com>
> Received: from mail.endhost.com ([unix socket])
> by endhost (Cyrus v2.1.18-IPv6-Debian-2.1.18-1) with LMTP; Wed, 27 Apr 2005 13:20:34 +0200
> X-Sieve: CMU Sieve 2.2
> Received: from localhost (endhost [127.0.0.1])
> by mail.endhost.com (Postfix) with ESMTP id 82D6BD000C
> for <firstname.lastname@example.org>; Wed, 27 Apr 2005 13:20:34 +0200 (CEST)
> Received: from mail.endhost.com ([127.0.0.1])
> by localhost (mail.endhost.com [127.0.0.1]) (amavisd-new, port 10024)
> with LMTP id 08140-06 for <email@example.com>;
> Wed, 27 Apr 2005 13:20:28 +0200 (CEST)
> Received: from test (endhost [127.0.0.1])
> by mail.endhost.com (Postfix) with ESMTP id C80C4D0004
> for <firstname.lastname@example.org>; Wed, 27 Apr 2005 13:19:20 +0200 (CEST)
> X-Mailbox-Line: From email@example.com
< X-Spam-Status: No, hits=0.7 tagged_above=-99.0 required=5.0 tests=AWL,
> X-Virus-Scanned: by amavisd-new-20030616-p10 (Debian) at endhost.com, maintained by CIDEV v.o.f.
> X-Spam-Status: No, hits=0.8 tagged_above=-99.0 required=5.0 tests=AWL,
If you've got any ideas why this works for me but not for the original recipient, please let me know!
Update The IRC channel helped me, I had to disable HTML viewing. The code for this is apparantly a bit buggy, but it's being rewritten. The other account had HTML display standard but my own account didn't have it, so that's why it worked for me but not for him.