Date: Wed, 17 Nov 1999 11:40:03 +0100 From: "James A Wilde" <james.wilde@telia.com> To: <freebsd-questions@freebsd.org> Subject: Corruption of file attachments passing late BSD relayers Message-ID: <015a01bf30e8$1c8298d0$8c0aa8c0@hk.tbv.se>
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Digest: This message reports on the corruption of file attachments in messages passing certain BSD UNIX mail exchangers. The corruption = affects messages sent using Microsoft Outlook and Outlook Express mail = clients. It may affect other clients also The corrupted file = attachments are about 30% larger than the non-corrupted form. A small = part of the increase appears to be the insertion of CRLF at 76 character = intervals. I have reported this as a bug to FreeBSD.org but one of low = priority. Problem description: My employer company's new mail system comprises a Microsoft Exchange = server version 5.5 SP2 protected by a FreeBSD UNIX version 2.2.5 firewall = running TIS Firewall Tookit. Clients are Microsoft Outlook 98 (plus a few cases = of Outlook 97), Microsoft Outlook Express, mostly version 4 but in some = cases version 5, and Microsoft Internet Explorer versions 4 or 5 using Outlook = Web Access. Most Outlook and Outlook Express clients are configured for Internet Only use and for IMAP mailboxes. All the clients on which = tests have been performed are configured in this way. The internal clients = use the FreeBSD machine as their smtp server. The system has run very satisfactorily for about a year and a half. About three weeks ago a new smtp server was installed outside the = firewall. This runs FreeBSD UNIX version 3.1. Almost immediately reports began to come in of corrupted file attachments. Hitherto only Microsoft Word and Excel documents have been examined since these were readily available. = The new smtp server was at first assumed to be the cause and was taken out = of the system, whereupon the level of reports reduced drastically but did = not disappear altogether. Upon further investigation it appears that the problem has arisen spasmodically since at least the beginning of October 1999, and the assumption that it was solely associated with the = installation of the new smtp server was proved to be false. However, the significant increase in reports when the new server was introduced into the system = and equally significant reduction was taken to indicate a strong causal relationship. Further investigation confirmed that the problem had not disappeared = with the removal of the smtp server. Mail passing in one direction from an account with one local Internet service provider to our company Exchange server could be relied upon to corrupt file attachments provided the = client program was configured for html format. Mail passing out from our = Exchange server to the same account was apparently not affected. Mail to and = from accounts with two other major Internet service providers passed = without corruption of the file attachments. File attachments to mail = from our Exchange server back to our Exchange server routed via the new = smtp server were also corrupted in a reproducible manner. This latter = fact confirmed that version 3.1 of FreeBSD UNIX was one of the factors = causing the corruption. The discovery that the ISP which corrupted file = attachments also uses a BSD variety of UNIX on their mail exchangers - it is not at present known which variety of BSD = is involved - whereas both the other ISPs use Sun Solaris UNIX = strengthens the hypothesis that the problem lies in late versions of BSD = UNIX. One further item of information which may be relevant is that the = ISP which corrupted file attachments also uses Exchange server for customers' mailboxes. What I have done: I have made extensive tests of sending mail with file attachments from = one internal account and three external accounts with different ISPs to the other accounts. I have tested the sending of mail with file attachments via the smtp = server running FreeBSD UNIX version 3.1 I have established that the corruption only happens when the clients are configured for html format, which is, of course, the default for Outlook Express but not for Outlook in which the default is plain text unless = the installer accepts the suggestion that Microsoft Word be used as the = email editor. What I have not done: I have not tested all the configurations of html format (no coding, = quoted printable, base64, allow 8-bit headers and allow only English headers in replies) formally but a simple test indicates that it is the selection = of html format rather than its detailed configuration which causes the = problem. I have not tested non-Microsoft mail client programs. I do not have the resources to do so, since my company only uses Microsoft mail clients. I have not tested file attachments other than Microsoft Word and = Microsoft Excel since no others have been reported and since these two products = are our most significant generators of file attachments. I have not tested different versions of BSD UNIX to see in which version = the problem arose. I have not tested whether the existence of an Exchange server at both = ends of the link is significant but the fact that the problem is = unidirectional suggests that it is not significant. On the other hand, the fact that = only the ISP using Exchange server for client mailboxes can reproduce = the problem suggests a link also to Exchange server. I have not thoroughly tested OWA. I can confirm that OWA mail from our Exchange server to our Exchange server is not affected. I have not ascertained how widespread the problem is. I do know that = mail from our branch offices to the home office and vice versa were affected during the time the new smtp server was in place, and not since. Mail = from outsiders to our company was and is occasionally affected but I have not been able to determine a pattern. Similarly mail from us to outsiders = was and is occasionally affected but again I have not been able to determine = a pattern. I do not know why file attachments in mail from the affected ISP to our Exchange server are corrupted but not file attachments in mail = travelling in the reverse direction. The workaround is, of course, to reconfigure all clients for plain text format. However, this only affects internal mail. We can not make = external users change their configuration of the client program. Since = a very high percentage of all users of email can be expected to use = Microsoft products and since apparently only some varieties of UNIX are = involved I suspect it will be easier to change the behaviour in the UNIX = end than in the Microsoft end. I have kept my results including the messages themselves, together with headers, of course. These can be examined for further relevant = information if required. Of course the problem could be one of bad configuration of a) our new = BSD smtp server and the ISPs mail exchangers or b) our Exchange server = or both. mvh/regards James Wilde Mail and DNS administrator TBV Head Office Box 5368 102 49 Stockholm Sweden Tel: +46 (8) 782 9283 Fax: +46 (8) 667 7249 Mobile: +46 (70) 546 6970 To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-questions" in the body of the message
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