As you may recall, an email service provider is a service where your users may receive their email. The most common, and most likely the largest percentage of your list, will be Hotmail, Gmail, Yahoo! Mail, and AOL. However, you should certainly check your email marketing database to see if you have any other email service providers who account for a significant portion of your database.
Why Segment by Email Service Provider?
There are two primary reasons to segment by email service provider. The first is to take advantage of (or avoid having your email template broken by) the various display options available in certain email service providers. The second reason is to be able to easily and nimbly recognize and respond to potential spam folder deliveries to certain major email service providers.
Email Service Provider Display: Most email service providers will block images from displaying. However, Yahoo! Mail commonly does not. This means that, if you segment your list out by Yahoo! Mail addresses, you can design a separate, more image-heavy template for those users while using a more text-based and html-based email template for other email service providers. You may find, as times change, that other email service providers change their regulations on images to your benefit or detriment. In either case, being able to develop and send a template specific to the display methods of the email service provider can improve your overall performance.
Controlling Spam and Deliverability: If you do not segment your email list by email service provider and are suddenly flagged as spam or junk mail at one email service provider, it may be several sends before you recognize it. You'll certainly see a decrease in your open rate if a specific email service provider is sending you to the junk folder, but it may take several email sends before you realize it is a deliverability problem and not simply a poorly written subject line. However, if you segment your email list by email service provider, then you will notice if only one segment of the list has a significant open rate drop off in a given send. If that happens, not only can you be fairly sure that you were flagged as spam or junk mail, but you already have the portion of the list segmented to respond to. You can decide to not send to that segment for a period of time or to send only a text-based version of your email to increase the chance that it will not be flagged as spam or junk.
Best Practices for List Segmentation by Email Service Provider
If you are going to segment your email marketing list by email service provider, chances are that you will later find yourself sub-segmenting by one of the other categories that we are about to discuss. Simply be sure to keep a careful eye on which lists are which to avoid duplicate email sends or over-sending to a single individual.
Also, be sure to regularly check in to ensure that a particular email service provider still accounts for enough of your list to warrant having its own email list segment.