Deliverability problems arise, for example, when an email address no longer exists, or the destination network is down for maintenance.
Those managing incoming email (like Yahoo! Mail or a corporate IT department) also review messages to determine whether to delete the email as spam, deliver it to the recipient's inbox or deliver it to the recipient's junk email folder.
This automated review process isn't perfect, so legitimate marketing messages can sometimes get tagged as spam and quietly deleted: another big issue in deliverability.
You'll find a lot of jargon in deliverability, so here are some simple explanations for six common terms.
You'll find a lot of jargon in deliverability, so here are some simple explanations for six common terms.
Anti-spam technologies refer to any automated process used to examine incoming mail with the specific intention of sorting the spam or "unwanted" email from the legitimate or "wanted" mail.
Spam filters review an email and see if it ticks enough boxes on the "this is spam" checklist. If it does, it gets "filtered out" from the main email delivery flow and deleted or redirected to a junk folder.
1. Spam reports or complaints
Most email software and webmail services give their users the option to mark an email as spam or junk mail, usually by clicking a "report spam" or "junk" button.
Software and services use these "spam reports" or "spam complaints" to refine their spam filters. In particular, if a service like Windows Live Hotmail sees that a sender is getting an unusually high number of spam complaints, then they will stop delivering any further emails from that sender.
2. Blacklists
A blacklist is a list of bad senders: those who are known to be sources of spam, particular those whose emails produce a large number of spam complaints. Some blacklists are kept by individual organizations for their own use. Others are public and can be used by any organization processing email.
When an email arrives from a blacklisted sender, then it's immediately tagged as spam and treated accordingly.
3. Whitelists
As you might guess, a whitelist is the converse of a blacklist: it's a list of good senders who are known to be a source of legitimate email.
An email coming from a whitelisted sender will usually bypass many of the spam filters and tests, and may get other kinds of preferential treatment. An organization may have its own whitelist or use a public one run by a third party.
4. Email certification
Email accreditation organizations review your email practices to see if they conform to a set of quality standards. If you pass this audit, then they certify your emails.
Email receivers like Yahoo! Mail and providers of anti-spam technologies have agreements with certification agencies allowing certified email to get priority treatment en route to the inbox.
5. Email authentication
Email authentication is where outgoing email is tagged in such a way that those systems receiving the email can accurately and reliably identify the true source.
6. Email sender reputation
Previously, most anti-spam technologies would look at an email's content to decide if it was spam or not. Today, more weight is given to the source of the email and the reputation of that source, as defined by its email practices.
As an example, a sender who rarely ever gets spam complaints and always emails active, up-to-date email addresses is likely to have a good sender reputation. Those senders with the best reputation have a better chance of getting email delivered.