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That’s How the TidBITS Email Bounces

One of the major advantages to us in moving all of our mailing lists over to our new Web Crossing-based server is that subscribers can centralize all their subscriptions under a single user account. That way, if you want to change your email address, you can change it just once, without any help from us, and every one of our TidBITS and Take Control mailing lists will automatically use the changed address. Refer to our Account Help page for instructions on changing your address, if you want to do that.


However, far too many people stop using email addresses without bothering to update their mailing list subscriptions. Perhaps the subscriber deletes the old account outright, or just abandons it, leaving it to accept mail until it exceeds its disk quota, at which point it starts rejecting new messages. Or perhaps the ISP deletes the unused address in a regular sweep. Whatever the specifics, the result on our end is that we attempt to send that address an issue of TidBITS, or messages from TidBITS Talk, or announcements of a free update to a Take Control ebook, and the messages are bounced back to us as being undeliverable.

In the past, bounces in response to TidBITS issues went to a special account, and once a week, Geoff Duncan downloaded the entire mailbox and processed it using a HyperCard-based utility he wrote called Hired Thug to identify bouncing addresses and remove them from our lists. Hired Thug was pretty good, but the sheer diversity of TidBITS’s mailing list and server setups prior to Web Crossing meant using Hired Thug wasn’t very practical for TidBITS Talk, the Take Control mailing lists, or our translations. I mostly handled bounces for those lists by hand, and, believe me, processing bounces is not a fun way to spend time.


Web Crossing runs its mailing lists a bit differently so it can better automate bounce processing, relying on a technique called variable envelope return paths (VERPs). With VERPs, every message is sent from a different envelope sender address, which is essentially the sender’s address at the SMTP protocol level. (Like physical letters, email messages are actually sent inside virtual envelopes, but these envelopes are seen only by SMTP servers, and the addresses used for the envelope aren’t necessarily the same as those you see in the To and From lines of the message.) Web Crossing’s envelope sender addresses look like <[email protected]>, and they uniquely identify both the intended recipient and the message being sent. If your mail server rejects or bounces a message from us, Web Crossing takes note of the envelope sender address, parses it to identify the user, and increments a counter that tracks how many bounces it has received from your email address. When your address exceeds three bounces over three separate days, your TidBITS account is marked as bouncing and we stop sending you email. In other words, if you’re subscribed only to the weekly announcements of TidBITS, it will typically take three weeks for your account to be marked as bouncing (barring special issues and our occasional week off); if you’re subscribed to the daily traffic on TidBITS Talk, you could be bounced within three days.


To be clear, when your TidBITS account is marked as bouncing, you won’t receive postings from any of our lists, but you’re still subscribed to the lists. That allows us to avoid delivering to bouncing addresses, but also allows you to log in to your account via the Web and either tell our system that your address is working again or change your email address to one that does work. So, if you think you missed an issue of TidBITS or haven’t received TidBITS Talk in a few days, the first thing you should do (after checking your spam filter!) is to log in and see if your account has been marked as bouncing. Again, see our Account Help page for instructions on logging in and changing email addresses. As long as you log in using the appropriate link provided on our Account Help page, Web Crossing will prompt you to verify your address automatically.


Bounces are an immense problem for mailing lists. We see 1 to 2 percent of addresses bounce in any given week, which is hundreds of addresses when you have lists the size of ours. In the past, we did our best to identify bounces and remove bouncing addresses from our lists, but once that was done, the only way someone could recover from a temporary problem was to resubscribe or contact us for help. Now that you can all manage your own TidBITS accounts via the Web, you can recover from a temporary delivery problem all on your own, which frees up our time so we can concentrate on creating new TidBITS content.

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