Troubleshooting Outlook Express for Mac OS 9: Problems cropping up with cable connections

Several MacFixIt readers have reported a strange phenomenon suddenly appearing in the past few weeks where sending messages above a certain size (with attachments or not) through Outlook Express is problematic.

David Sirola writes "About 3 weeks ago a problem developed using Outlook Express and sending attachments. No matter the size of the attachment, 79K or 3megs, the mail seems to stall at 30 KB to 40 KB. Sometimes it seems to make small progress over an hour, or sometimes it will issue an error -3155. I've tried RR support with no luck. I've re-built OE databases, tossed preferences, re-installed the software, pram zap, all with no results. It's getting out of control, since I'm a designer and I need to send files."

There are at least a dozen corroborating reports of this problem, with virtually readers confirming that any messages over 25-30 KB cause problems. Oddly, all of the reports originate from users with Cable-based Internet Access.

Error -3155 indicates an Apple OpenTransport error code.

UPDATE: Kristin Green found this interesting note on an ISP page support page, indicating that MTU problems may be to blame for size restrictions from some cable providers: "MTU problems cause severe lags in network logon times, cause email attachments and other functions within Outlook to fail, and cause applications to stop functioning entirely. Note that, by default, the MTU on Windows operating systems is 1500 (Ethernet) and that a change to 1492 may resolve some, but not all, problems."

You can manually set the MTU value for en0 or en1 by doing "/sbin/ifconfig en0 mtu 1492" (or en1, depending on your interface). The MTU will be reset on the next reboot. Of course, this will only help if your are running Outlook Express in Classic mode. See Knowledge Base article #107474 for more information.

If you have had success changing your MTU setting, or have any additional information, please drop us a line at late-breakers@macfixit.com.

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