You may not have heard of VERP, but it is very important that you find out whether your email campaign software/service uses it.
Variable Envelope Return Path or "VERP" is a technique to enable automatic detection and removal of undeliverable e-mail addresses.
I have previously used email campaign software (mentioning no names) whereby VERP was not utilised.
Let me give you a scenario to highlight why you need to check VERP is being used..
Say you have a newsletter sign-up box on a site. 100 people sign-up but 99 of them are invalid; people move companies, change email addresses, give fake addresses etc all the time (especially if the email address is not validated). You create and send your email campaign (with a system not using VERP or equivalent) to the theoretical 100 people (actually only 1 person will ever receive it). That loyal user actually views/reads/clicks the email you sent - you check your campaign stats and it says your email campaign reach was 1% - very disappointing.
If the system used VERP that reach would be accurate and report a 100% reach.. as it has taken into account the Users that never existed (or no longer exist).
On top of this, the next time the campaign is sent, it will only send to the subscribed members (1 person) rather than not learning and resending to the 99 non-existent people.
It sounds obvious but not all email campaign web sites/tools use VERP.
So how does it work?
VERP works by using a different return path (also called "envelope sender") for each recipient of a message. If a *permanent* bounce is received by that unique return path then the system knows it can automatically un-subscribe that user from the list.
Note: It is important to distinguish a permanent bounce from a temporary bounce (out of office, over quota etc).
Recipient: firstname.lastname@example.org Envelope Sender: email@example.com
Recipient: firstname.lastname@example.org Message: Example.com was not able to deliver this email as the recipient email@example.com does not exist.
[firstname.lastname@example.org is unsubscribed from mailing lists, and is no longer sent emails from said software]
At Clock we built an online email and SMS campaign website a number of years ago, called ClockUp and we made sure we utilised VERP from the very beginning, we realised during development that the stats we provided to our clients without using VERP would be very wrong.
There are a number of good email campaign sites out there; MailChimp, DotMailer, CampaignMonitor to name a few, I believe they use VERP (or a similar method).. whatever you use, it's worth checking.
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