We state that it’s not possible to validate emails hosted on a minority of Microsoft Exchange servers.
Here’s why:
Scope
This issue:
- Affects a small number of remote mail servers using MS Exchange. (i.e. whether you use Exchange internally is of no consequence as our service is totally independent of your infrastructure).
- Affects all email validation service (i.e. our services & all of our competitors)
Description
On rare occasions, we have found that some email address validations come back as “Ok” when, in fact they are “Invalid”. This can lead to a small margin (we estimate around 5%) of error in overall validation accuracy. This means that, you may receive a very small number of email bounces from your “cleansed” email lists.
Cause
A “default” installation (as most are) of MS Exchange does not cause this problem.
However, as part of spam management functionality, Microsoft has made available various configuration options to Exchange System Administrators. One of these options is called “SMTP Filtering” which, if enabled, prevents any email checking service from being able to determine if an email address is valid or not. More technical info can be found here (see section called “SMTP Filtering Layer”).
[As a side note of interest, we have determined that Microsoft (*.microsoft.com emails) who use Exchange do not have the "SMTP Filtering" option enabled. Read into this what you will:)]
What this means
In terms of the overall validation process, this is one of the reasons why no-one can guarantee 100% accuracy with this type of validation process. We know (from extensive testing and having run other email validation services for several years) that the effect of this problem is relatively small in the overall scheme.
From your perspective, the worst case scenario is that you get a small percentage of emails passed through the “ok” filter that then subsequently get “bounced” (i.e. returned to you with a Non Delivery Report [NDR]) when you send an email to an address hosted on some Exchange servers.
Taking into account this known issue (together with others), we state that our validation service provides between 85-90% overall accuracy which we believe is the best achievable (see comparison). Additionally, we are so confident that we deliver the best accuracy possible, that we back this up with a money back guarantee.
If you have any email addresses that are of particular concern, you can check these out using our free online checker which will give you an idea of what results to expect from our “bulk” checker.
