Does email have a guarantee of delivery?

A client asked me earlier this week what SLAs ISPs provided for email delivery. The short answer is that there isn’t a SLA and that the only guarantee is that the email will get there when it gets there.
But as I was mentioning this to Steve, he pointed out that there was a recent change in the RFCs for email. In both RFC 821/2 and RFC 2821/2 (the original email related RFCs and the update in the early 2000’s) the RFCs stated that once a receiving MTA accepted an email that that MTA was required to either delivery the mail or generate an asynchronous bounce. While this isn’t a standard SLA, it does mean that a 2xy response after DATA meant the email would either be delivered to the user or be sent back to the sender. Despite the RFC requirements some receivers would still drop mail on the floor for various reasons, sometimes intentionally and sometimes not.
RFC 5321/2, the current SMTP standard, still says that once a server accepts the mail it must not lose that mail ‘for frivolous reasons.’ The RFC goes on to admit, though, that in recent years, SMTP servers are under a range of attacks and dropping mail on the floor is not frivolous in those cases.
 

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Email is store and forward

Many of us are so used to email appearing instantaneous, we forget that the underlying protocol was never designed for instant messaging. When the SMTP protocol was originally proposed it was designed to support servers that may have had intermittent connectivity. The protocol allowed for email to be spooled to disk and then sent when resources were available. In fact, almost everyone who was around more than 10 years ago knows of a case where an email took weeks, months or even years to deliver.
These days we’re spoiled. We expect the email we send to friends and relatives to show up in their mailbox within moments of sending it. We expect that sales receipt or e-ticket to show up in our mailbox within instants of a purchase. We expect that our ISPs will get us email immediately, if not sooner.
But there are a lot of things that can slow down email delivery. At several points in the process an email may be spooled to disk. It stays on the spool until the next part of the delivery process can happen. Other points of slowdown include the various anti-spam, anti-virus and anti-phishing protections that ISPs must implement. Then add in the extreme volume of email (around 10 billion messages a day) and all of a sudden email delivery is slower than many senders and recipients expect it to be. This delay is not ideal, but the system is designed so that mail is not silently discarded.
While individual emails may be delayed, most users will rarely see that delay in the email that they send. Bulk senders, who may be sending thousands or hundreds of thousands of emails a day, may see more delays in a single send than the average user sees in years of sending one-to-one email.
Email is store and forward, not instant. Sometimes that means there is a delay in getting email into the recipients inbox. And, sometimes there isn’t anything anyone can do to speed up delivery, except to adjust expectations of how email works.

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Delivery emergencies and the holidays

There is a lot of contention between ISPs and senders at the best of times. As we move into the holiday season, retailers are increasing their email marketing, sometimes quite significantly. This causes more delivery issues as recipients and MTAs react to the increased volume.
At many non retail companies, however, the pace of work slows down. There are distractions and office parties and people taking long lunches to finish their holiday shopping. Non-critical departments are not staffed for official holidays like Thanksgiving and Christmas Day.
This means that delivery issues may not be responded to as quickly as senders might like. Just this morning I got a call from someone who wants his delivery issues to be fixed by tomorrow. I’m sorry, even if I were to treat this as an emergency, there is work and investigation that needs to be done at the ISP end, and they’re not necessarily going to have a staffed delivery desk on Thanksgiving day. And even if they do have a staffed desk, it’s possible the staff won’t be focused and issues won’t be handled as fast as they might otherwise be.
I’d love to help, but there’s a limit to what I can do. Filtering decisions are made by the ISP, or their filter vendor, and sometimes they don’t happen as fast as we’d like. It’s frustrating for senders to have to deal with, but these are the realities of email delivery.

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Spamhaus answers questions

Lost in all of the DOS attack news this week is that the first installment of Spamhaus answering questions from marketers in Ken Magill’s newsletter.
It’s well worth a read for anyone who is interested in hearing directly from Spamhaus.
One quote stood out for me, and it really sums up how I try to work with clients and their email programs.

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